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Class __S.S_9l[__ 
Book ' S ^ — 



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copyRiGHT DEPOsrr. 



SOILS AND FERTILIZERS 



THE MACMILLAN COMPANY 

NEW YORK • BOSTON • CHICAGO 
ATLANTA • SAN FRANCISCO 

MACMILLAN & CO., Limited 

LONDON ■ BOMBAY ■ CALCUTTA 
MELBOURNE 

THE MACMILLAN CO. OF CANADA, Ltd. 

TORONTO 



SOILS AND FERTILIZERS 



BY 



HARRY SNYDER, B.S. 

PROFESSOR OF AGRICULTURAL CHEMISTRY AND SOILS 
UNIVERSITY OF MINNESOTA 



THIRD EDITION 



THE MACMILLAN COMPANY 
1908 

, All rights reserved 



UBWARV of CONGRESS 
I wo Oooies neceotxi 

JUN 23 iy08 

OLASS A \XC. Nv 

COPY B. 



b' 






^^ 



Copyright, 1908, 
By the MACMILLAN COMPANY. 



Set up and electrotyped. Published June, 1908. 



J. S. Gushing Co. — Berwick & Smith Co. 
Norwood, Mass., U.S.A. 



PREFACE TO THIRD EDITION 

This work is the outgrowth of instruction given at 
the University of Minnesota to young men who intend 
to become farmers and who desire information that will 
be of assistance to them in their profession. At first 
mimeographed notes were prepared, which were later 
published under the title " The Chemistry of Soils and 
Fertilizers." This was revised, enlarged, and published 
as " Soils and Fertilizers." With the extension of 
various lines of investigation relating to soils, a sec- 
ond revision and enlargement of the book has become 
necessary. It is the aim to present in condensed form 
the principles of the various sciences, particularly chem- 
istry, which have a bearing upon the economic produc- 
tion of crops and the conservation of the soil's fertility. 
The work as now presented includes all the topics 
and the laboratory experiments relating to soils, as out- 
lined by the Committee on Methods of Teaching Agri- 
culture, of the Association of Agricultural Colleges and 
Experiment Stations. 

HARRY SNYDER. 

University of Minnesota, 
College of Agriculture, 

St. Anthony Park, Minnesota, 

March i, 1908. 



CONTENTS 

PAGES 

Introduction i-io 

Early uses of manures and explanation of their action 
by alchemists ; Investigations prior to 1800 : Work of De 
Saussure, Davy, Thaer, and Boussingault ; Liebig's writ- 
ings and their influence ; Investigations of Lawes and Gil- 
bert ; Work of Tull ; Contributions of other investigators ; 
Agronomy; Value of soil studies. 

CHAPTER I 

Physical Properties of Soils 11-53 

Chemical and physical properties of soils considered ; 
Weight of soils ; Pore space ; Specific gravity ; Size of soil 
particles ; Clay ; Sand ; Silt ; Form of soil particles ; Num- 
ber and arrangement of soil particles ; Mechanical analysis 
of soils ; Crop growth and physical properties. Soil types : 
Potato and truck soils ; FrUit soils ; Corn soils ; Me- 
dium grass and grain soils ; Wheat soils ; Sandy, clay, 
and loam soils. Relation of the soil to water ; Amount of 
water required for crops ; Bottom water ; Capillary water ; 
Hydroscopic water ; Loss of water by percolation, evapo- 
ration, and transpiration ; Drainage ; Influence of forest 
regions ; Influence of cultivation upon the water supply 
of crops ; Capillary water and cultivation ; Shallow surface 
cultivation ; Cultivation after rains ; Rolling ; Subsoiling ; 
Fall plowing; Spring plowing; Mulching; Depth of 
plowing ; Permeabijity of soils ; Fertilizers and their in- 



Viii CONTENTS 

PAGES 

fluence upon moisture content of soils ; Farm manures 
and soil moisture ; Relation of soils to heat ; Heat re- 
quired for evaporation ; Influence of drainage upon soil 
temperature ; Specific heat of soils ; Cultivation and soil 
temperature ; Heat from chemical reactions within the 
soil ; Heat and crop growth ; Organic matter and iron 
compounds; Color of soils ; Odorand taste of soils ; Power 
to absorb gases ; Relation of soils to electricity ; Impor- 
tance of physical properties of the soil. 

CHAPTER II 

Geological Formation and Classification of Soils 54-70 
Agricultural geology ; Formation of soils ; Action of 
heat and cold ; Action of water ; Glacial action ; Chem- 
ical action of water ; Action of air and gases ; Action of 
microorganism ; Action of vegetation ; Action of earth- 
worms ; Action of wind ; Combined action of the various 
agents ; Distribution of soils ; Sedentary and transported 
soils ; Rocks and minerals from which soils are derived, 
as quartz, feldspar, mica, hornblende, zeolites, granite, 
apatite, limestone, kaolin ; Disintegration of rocks and 
minerals ; Value of geological study of soils. 

CHAPTER III 

The Chemical Composition of Soils . . . 71-115 
Elements present in soils ; Classification of elements ; 
Combination of elements ; Forms in which elements are 
present in soils ; Acid-forming elements, silicon, double 
silicates, carbon, sulphur, chlorine, phosphorus, nitrogen, 
oxygen, hydrogen ; Base-forming elements, aluminum, 
potassium, calcium, magnesium, sodium, iron ; Forms of 
plant food ; Amount of plant food in different forms in 



CONTENTS IX 

. PAGES 

various types of soils ; Acid soluble matter of soils ; Acid 
insoluble matter ; Action of organic acids upon soils ; How 
a soil analysis is made ; Value of soil analysis ; Interpre- 
tation of the results of soil analysis ; Use of dilute acids 
as solvents in soil analysis ; Use of dilute mineral acids in 
soil analysis ; Available and unavailable plant food ; Vola- 
tile matter of soils ; Distribution of plant food in the soil ; 
Composition of typical soils ; ' Alkali ' soils and their 
improvement ; Acid soils ; Organic compounds of soil ; 
Sources ; Classification ; Humus ; Humates ; Humifica- 
tion ; Humates produced by different kinds of organic 
matter; Mineral matter combined with humus; Value of 
humates as plant food ; Amount of plant food in humic 
forms ; Physical properties of soils influenced by humus ; 
Loss of humus by forest fires, by prairie fires, by cultiva- 
tion ; Humic acid ; Soils in need of humus ; Soils not in 
need of humus ; Composition of humus from old and new 
soils; Influence of different methods of farming upon 
humus. 

CHAPTER IV 

Nitrogen of the Soil and Air, Nitrification, and Ni- 
trogenous Manures 1 16-157 

Importance of nitrogen as plant food ; Atmospheric ni- 
trogen as a source of plant food. Experiments of Bous- 
singault, Ville, Lawes and Gilbert, and Atwater ; Result 
of field trials ; Experiments of Hellriegel and Wilfarth 
and recent investigators ; Composition of root nodules ; 
Amount of nitrogen returned to soil by leguminous crops 
and importance to agriculture ; Nitrogenous compounds 
of the soil ; Origin ; Organic nitrogen ; Amount of nitro- 
gen in soils ; Removed in crops ; Nitrates and nitrites ; 
Ammonium compounds ; Ammonia in rain and drain 



X CONTENTS 

PAGES 

waters ; Ratio of nitrogen to carbon in the soil ; Losses 
of nitrogen from soils ; Gains of nitrogen to soils ; Nitri- 
fication : Former views regarding ; Workings of an organ- 
ism ; Conditions necessary for nitrification ; Influence of 
cultivation upon these conditions ; Nitrous acid organisms, 
ammonia-producing organisms, denitrification, number and 
kind of organisms in soils ; Inoculation of soils with 
organisms ; Chemical products produced by organisms ; 
Losses of nitrogen by fallowing rich prairie lands ; Influ- 
ence of plowing upon nitrification ; Nitrogenous manures ; 
Sources ; Dried blood, tankage, flesh meal, fish scrap, 
seed residue, and uses of each ; Leather, wool waste, and 
hair ; Available organic nitrogen ; Peat and muck ; Le- 
guminous crops as nitrogenous fertilizers ; Sodium nitrate, 
ammonium salts ; Calcium cyanamid ; Cost and value of 
nitrogenous fertilizers. 

CHAPTER V 

Farm Manures 158-190 

Variable composition of farm manures ; Average com- 
position of manures ; Factors which influence composition 
of manures ; Absorbents ; Use of peat and muck as ab- 
sorbents ; Relation of food consumed to manures pro- 
duced ; Bulky and concentrated foods ; Course of the 
nitrogen of the food during digestion ; Composition of 
liquid and solid excrements ; Manurial value of foods ; 
Commercial valuation of manure ; Influence of age and 
kind of animal ; Manure from young and old animals ; 
Cow manure ; Horse manure ; Sheep manure ; Hog ma- 
nure; Hen manure ; Mixing manures ; Volatile products 
from manure ; Human excrements ; Preservation of ma- 
nures ; Leaching ; Losses by fermentation ; Different kinds 
of fermentation ; Water necessary for fermentation ; Heat 



CONTENTS XI 

PAGES 

produced during fermentation ; Composting manures ; 
Uses of preservatives ; Manure produced in sheds ; Value 
of protected manure ; Use of manures ; Direct hauling to 
field ; Coarse manures injurious ; Manuring pasture land ; 
Small piles of manure in fields objectionable ; Rate of 
application ; Most suitable crops to apply to ; Compara- 
tive value of manure and food ; Lasting effects of manure ; 
Comparative value of good and poor manure ; Summary 
of ways in which manures may be beneficial. 

CHAPTER VI 

Fixation igi-197 

Fixation a chemical change, examples of; Fixation and 
absorption ; Due to zeolites ; Humus and fixation ; Soils 
possess diff"erent powers of fixation ; Nitrates do not 
undergo fixation ; Fixation of potash, phosphoric acid, 
and ammonia ; Fixation may make plant food less avail- 
able ; Fixation a desirable property of soils ; Fixation and 
the action of manures ; Fixation and soil solution. 

CHAPTER VII 

Phosphate Fertilizers 198-2 11 

Importance of phosphorus as plant food ; Amount re- 
moved in crops ; Amount and source of phosphoric acid 
in soils ; Commercial forms of phosphoric acid ; Phosphate 
rock ; Calcium phosphates ; Reverted phosphoric acid ; 
Available phosphoric acid ; Manufacture of phosphate 
fertilizers, acid phosphates, superphosphates ; Commercial 
value of phosphoric acid ; Basic slag phosphate ; Guano ; 
Bones ; Steamed bone ; Dissolved bone ; Bone black ; 
Fineness of division of phosphate fertilizers ; Use of 
phosphate fertilizers ; How to keep the phosphoric acid 
of the soil available. 



Xii CONTENTS 

CHAPTER VIII 

PAGES 

Potash Fertilizers 212-222 

Potassium an essential element ; Amount of potash re- 
moved in crops ; Amount in soils ; Source of soil potash ; 
Commercial forms of potash ; Stassfurt salts, occurrence 
of; Kainit; Muriate of potash ; Sulphate of potash ; Other 
Stassfurt salts; Wood ashes, composition of; Amount of 
ash in different kinds of wood ; Action of ashes on soils ; 
Leached ashes ; The alkalinity of ashes ; Coal ashes ; 
Miscellaneous ashes ; Commercial value of potash ; Use 
of potash fertilizers ; Joint use of potash and lime. 

CHAPTER IX 

Lime and Miscellaneous Fertilizers . . . 223-232 
Calcium an essential element ; Amount of lime removed 
in crops ; Amount of lime in soils ; Different kinds of 
Hme fertilizers ; Their physical and chemical action ; Action 
of lin.e upon organic matter and in correcting acidity of 
soils ; Lime liberates potash ; Aids nitrification ; Action of 
land plaster on some ' alkali ' soils ; Quicklime and slaked 
lime ; Pulverized lime rock ; Marl ; Physical action of 
lime; Judicious use of lime; Miscellaneous fertilizers; 
Salt and its action on the soil ; Magnesium salts ; Soot ; 
Seaweed ; Strand plant ash ; Wool washings ; Street 
sweepings. 

CHAPTER X 

Commercial Fertilizers 233-254 

History of development of industry ; Complete fertili- 
zers and amendments ; Variable composition of commer- 
cial fertilizers ; Preparation of fertilizers ; Inert forms of 



CONTENTS Xm 



matter in fertilizers ; Inspection of fertilizers ; Mechanical 
condition of fertilizers ; Forms of nitrogen, phosphoric 
acid, and potash in commercial fertilizers ; Misleading 
statements on fertilizer bags ; Estimating the value of a 
fertilizer ; Home mixing ; Fertilizers and tillage ; Abuse 
of commercial fertilizers; Judicious use of; Field tests; 
Preliminary experiments ; Verif3^ing results ; Deficiency 
of nitrogen, phosphoric acid, potash, and of two elements ; 
Importance of field trials; Will it pay to use fertilizers? 
Amount to use per acre ; Influence of excessive applica- 
tions ; Fertilizing special crops ; Commercial fertilizers 
and farm manures. 

CHAPTER XI 

Food Requirements of Crops 255-272 

Amount of fertility removed by crops ; Assimilative 
powers of crops compared ; Ways in which plants obtain 
their food ; Cereal crops, general food requirements ; 
Wheat; Barley; Oats; Corn; Miscellaneous crops ; Flax; 
Potatoes ; Sugar beets ; Roots ; Turnips ; Rape ; Buck- 
wheat ; Cotton ; Hops ; Hay and grass crops ; Leguminous 
crops ; Garden crops ; Fruit trees ; Small fruits ; Lawns. 

CHAPTER XII 

Rotation of Crops and Conservation of Soil Fer- 
tility 273-290 

Object of rotating crops ; Principles involved in crop 
rotation ; Deep- and shallow-rooted crops ; Humus-con- 
suming and humus-producing crops ; Crop residues ; Ni- 
trogen-consuming and nitrogen-producing crops ; Rotation 
and mechanical condition of soil ; Economic use of soil 
water ; Rotation and farm labor ; Economic use of ma- 
nures ; Salable crops ; Rotations advantageous in other 



XIV CONTENTS 

PAGES 

ways ; Long- and short-course rotations ; Example of 
rotation ; Problems in rotations ; Conservation of fertility ; 
Necessity of manures ; Use of crops ; Two systems of 
farming compared ; Losses of fertility with different 
methods of farming ; Problems on income and outgo of 
fertility from farms. 

CHAPTER XIII 

Preparation of Soils for Crops .... 291-306 
Importance of good physical condition of seed bed ; In- 
fluence of methods of plowing upon the condition of the 
seed bed ; Influence of moisture content of the soil at the 
time of plowing; Influence upon the seed bed of pulver- 
izing and fining the soil ; Aeration of seed bed necessary ; 
Preparation of seed bed without plowing ; Mixing of sub- 
soil with seed bed ; Cultivation to destroy weeds ; Influ- 
ence of cultivation upon bacterial action ; Cultivation for 
special crops ; Cultivation to prevent washing and gully- 
ing of lands ; Bacterial diseases of soils ; Influence of 
crowding of plants in the seed bed ; Selection of crops ; 
Inherent and cumulative fertility of soils ; Balanced soil 
conditions. 

CHAPTER XIV 

Laboratory Practice 307-326 

General directions ; Note book ; Apparatus used in 
work ; Determination of hydroscopic moisture of soils ; 
Determination of the volatile matter ; Determination of 
the capacity of loose soils to absorb water ; Determination 
of capillary water of soils ; Capillary action of water upon 
soils ; Influence of manure and shallow surface cultivation 
upon moisture content and temperature of soils ; Weight 



CONTENTS XV 

PAGES 

of soils ; Influence of color upon the temperature of soils ; 
Rate of movement of air through soils ; Rate of move- 
ment of water through soils ; Separation of sand, silt, and 
clay; Sedimentation of clay; Properties of rocks from 
which soils are derived ; Form and size of soil par- 
ticles ; Pulverized rock particles ; Reaction of soils ; The 
granulation of soils ; Absorption of gases by soils ; Acid 
insoluble matter of soils ; Acid soluble matter of soils ; 
Extraction of humus from soils ; Nitrogen in soils ; Test- 
ing for nitrates ; Volatilization of ammonium salts ; Test- 
ing for phosphoric acid ; Preparation of acid phosphate ; 
Solubility of organic nitrogenous compounds in pepsin 
solution ; Preparation of fertilizers ; Testing ashes ; Ex- 
tracting water soluble materials from a commercial fertili- 
zer ; Influence of continuous cultivation and crop rotation 
upon the properties of soil ; Summary of results with tests 
of home soil. i 

Review Questions 327-339 

References 340-344 

Index 345-35° 



SOILS AND FERTILIZERS 



INTRODUCTION 

Prior to 1800 but little was known of the sources 
and importance of plant food. Manures had been 
used from the earliest times, and their value was recog- 
nized, although the fundamental principles underlying 
their use were not understood. It was believed they 
acted in some mysterious way. The alchemists had 
advanced various views regarding them ; one was that 
the so-called " spirits " left the decaying manure and 
entered the plant, producing more vigorous growth. 
As evidence, the worthless character of leached manure 
was cited. It was thought the spirits had left such 
manure. The terms 'spirits of hartshorn,' 'spirits of 
niter,' ' spirits of turpentine,' and many others reflect 
these ideas regarding the composition of matter. 

The alchemists held that one substance, as copper, 
could be changed to another substance, as gold. Plants 
were supposed to be water transmuted in some myste- 
rious way directly into plant tissue. Van Helmont, in 
the seventeenth century, attempted to prove this. " He 
took a large earthen vessel and filled it with 200 
pounds of dried earth. In it he planted a willow 



2 SOILS AND FERTILIZERS 

weighing 5 pounds, which he duly watered with rain 
and distilled water. After five years he pulled up the 
willow and it now weighed 169 pounds and 3 ounces."^ 
He concluded that 164 pounds of roots, bark, leaves, 
and branches had been produced by direct transmu- 
tation of the water. 

It is evident from the preceding example that any- 
thing like an adequate idea of the growth and compo- 
sition of plant bodies could not be gained until the 
composition of air and water was established. 

The discovery of oxygen by Priestley in 1774, of 
the composition of water by Cavendish in 1781, and 
of the role which carbon dioxide plays in plant and 
animal Hfe by De Saussure and others in 1800, formed 
the nucleus of our present knowledge regarding the 
sources of matter stored up in plants. It was between 
1760 and 1800 that alchemy lost its grip because of 
advances in knowledge and the way was opened for 
the development of modern chemistry. 

De Saussure's " Recherches sur la Vegetation," pub- 
lished in 1804, was the first systematic work showing 
the sources of the compounds stored up in plant bodies. 
He demonstrated, quantitatively, that the increase in the 
amount of carbon, hydrogen, and oxygen, when plants 
were exposed to sunlight, was at the expense of the 
carbon dioxide of the air, and of the water of the soil. 
He also, maintained that the mineral elements derived 
from the soil were essential for plant growth, and gave 
the results of the analyses of many plant ashes. He 



INTRODUCTION 3 

believed that the nitrogen of the soil was the main 
source of the nitrogen found in plants. These views 
have since been verified by many investigators, and are 
substantially those held at the present time regarding 
the fundamental principles of plant growth. They were 
not, however, accepted as conclusive at the time, and it 
was not until nearly a half-century later, when Bous- 
singault, Liebig, and others repeated the investigations 
of De Saussure, that they were finally accepted by chem- 
ists and botanists. 

From the time of De Saussure to 1835, scientific 
experiments relating to plant growth were not actively 
prosecuted, but the facts which had accumulated were 
studied, and attempts were made to apply the results 
to actual practice. Among the first to see the relation 
between chemistry and agriculture was Sir Humphry 
Davy. In 181 3 he published his "Essentials of Agri- 
cultural Chemistry," which treated of the composition 
of air, soil, manures, and plants, and of the influence 
of light and heat upon plant growth. About this 
period, Thaer published an important work entitled 
" Principes Raisonnes d' Agriculture." He believed 
humus determined the fertility of the soil, that plants 
obtained their food mainly from humus, and that the 
carbon compounds of plants were produced from the 
organic carbon compounds of the soil. This gave rise 
to the so-called humus theory, which was later shown 
to be an inadequate idea regarding the source of plant 
food, and for a time it prevented the actual value of 



4 SOILS AND FERTILIZERS 

humus as a factor of soil fertility from being recog- 
nized. The writings of Thaer were of a most prac- 
tical nature, and they did much to stimulate later 
investigations. 

About 1830 there was renewed interest in scientific 
investigations relating to agriculture. At this time 
Boussingault, a French investigator, became actively 
engaged in agricultural research. He was the first to 
have a chemical laboratory upon a farm and to make 
practical investigations in connection with agriculture. 
This marks the establishment of the first agricultural 
experiment station. Boussingault's work upon the as- 
similation of the free nitrogen of the air is reviewed in 
Chapter IV. His study of the rotation of crops was 
a valuable contribution to agricultural science. He dis- 
covered many important facts relating to the chemical 
characteristics of foods, and was the first to make a 
comparison as to the amount of nitrogen in differ- 
ent kinds of foods and to determine their value on the 
basis of the nitrogen content. His study of the pro- 
duction of saltpeter did much to prepare the way for 
later work on nitrification. The investigations of Bous- 
singault covered a variety of subjects relating to plant 
growth. He repeated and verified much of the earlier 
work of De Saussure, and also secured many additional 
facts regarding the chemistry of growth. As to the 
source of nitrogen in crops, he states : " The soil fur- 
nishes the crops with mineral alkaline substances, pro- 
vides them with nitrogen, by ammonia and by nitrates, 



INTRODUCTION 5 

which are formed in the soil at the expense of the nitrog- 
enous matter contained in diluvium, which is the basis 
of vegetable earth ; compounds in which nitrogen exists 
in stable combination, only becoming fertilizing by the 
effect of time." As to the absorption of the gaseous 
nitrogen of the air by vegetable earth, he says : " I am 
not acquainted with a single irreproachable observation 
that establishes it ; not only does the earth not absorb 
gaseous nitrogen, but it gives it off." ^ 

The investigations of DeSaussure and Boussingault, 
and the writings of Davy, Thaer, Sprengel, and Schiib- 
ler prepared the way for the work and writings of Lie- 
big. In 1840 he published "Organic Chemistry in its 
Applications to Agriculture and Physiology." Liebig's 
agricultural investigations were preceded by many valu- 
able discoveries in organic chemistry, which he apphed 
directly in his interpretations of agricultural problems. 
His writings were of a forceful character and were ex- 
tremely argumentative. They provoked, as he intended, 
vigorous discussions upon agricultural problems. He 
assailed the humus theory of Thaer, and showed that 
humus was not an adequate source of the plant's carbon. 
In the first edition of his work he noted that farms 
from which certain products were sold became less pro- 
ductive, because of the loss of nitrogen. In a second 
edition he considered that the combined nitrogen of 
the air was sufficient for crop production. He overesti- 
mated the amount of ammonia in the air, and underesti- 
mated the value of the nitrogen in soils and manures. 



6 SOILS AND FERTILIZERS 

A Study of the composition of ash of plants led him 
to propose the mineral theory of plant nutrition. 
De Saussure had shown that plants contain certain min- 
eral elements, but he did not emphasize their impor- 
tance as plant food. Liebig's writings on the composi- 
tion of plant ash, and his emphasizing the importance of 
supplying crops with mineral food, led to the commer- 
cial preparation of manures, which in later years devel- 
oped into the commercial fertilizer industry. The work 
of Liebig was not conducted in connection with field 
experiments. It had, however, a most stimulating in- 
fluence upon investigations in agricultural chemistry, 
and to him we owe, in a great degree, the summarizing 
of previous disconnected work and the mapping out of 
valuable lines for future investigations. 

Liebig's enthusiasm for agricultural investigations 
may be judged from the following extract : " I shall be 
happy if I succeed in attracting the attention of men 
of science to subjects which so well merit to engage 
their talents and energies. Perfect agriculture is the 
true foundation of trade a7id industry ; it is the founda- 
tion of the riches of states. But a rational system of 
agriculture cannot be formed without the application of 
scientific principles, for such a system must be based on 
an exact acquaintance with the means of nutrition of 
vegetables, and with the influence of soils, and actions 
of manures upon them. This knowledge we must seek 
from chemistry, which teaches the mode of investigat- 
ing the composition and of the study of the character of 



INTRODUCTION 7 

the different substances from which plants derive their 
nourishment."^ 

Soon after Liebig's first work appeared, the investi- 
gations at Rothamsted by Sir J. B. Lawes were under- 
taken. The most extensive systematic work in both 
field experiments and laboratory investigations ever 
conducted has been carried on by Lawes and Gilbert 
at Rothamsted, Eng. Dr. Gilbert had previously been 
a pupil of Liebig, and his becoming associated with 
Sir J. B. Lawes marks the establishment of the second 
experiment station. Many of the Rothamsted experi- 
ments have been continued since 1844, and results of 
the greatest value to agriculture have been obtained. 
The investigations on the non-assimilation of atmos- 
pheric nitrogen by crops, pubhshed in 1861, were ac- 
cepted as conclusive evidence upon this much-vexed 
question. Their work on manures, nitrification, the 
nitrogen supply of crops, and the increase and decrease 
of the nitrogen of the soil when different crops are pro- 
duced, has had a most important bearing upon main- 
taining the fertility of soils. 

" The general plan of the field experiments has been 
to grow some of the most important crops of rotation, 
each separately, for many years in succession on the 
same land, without manure, with farmyard manure, 
and with a great variety of chemical manures, the 
same kind of manure being, as a rule, applied year 
after year on the same plot. Experiments with differ- 
ent manures on the mixed herbage of permanent grass 



8 SOILS AND FERTILIZERS 

land, on the effects of fallow, and on the actual course 
of rotation without manure, and with different manures 
have likewise been made."^ 

In addition to Davy, Thaer, De Saussure, Boussin- 
gault, Liebig, and Lawes and Gilbert, a great many 
others have contributed to our knowledge of the prop- 
erties of soils. The work of Pasteur, while it did not 
directly relate to soils, indirectly had great influence 
upon soil investigations. His researches upon fermen- 
tation made it possible for Schlosing to prove that 
nitrification is the result of the workings of living 
organisms. These have since been isolated and studied 
by Warington and Winogradsky. 

The importance of the physical condition of the soil 
and its relation to crop production was recognized by 
agriculturists at about the same time that the sources 
of plant food were being investigated. Jethro Tull 
published in 1829 a work entitled "The Horse-Hoeing 
Husbandry," which emphasized the importance of 
thorough cultivation of the soil. That increase in the 
yield of crops, destruction of weeds, reduction of rust 
and blight of wheat, and general improvement of the 
soil, are all results of improved tillage is clearly set 
forth in Tull's work. Tull was inclined to believe that 
tillage could take the place of manure. " All sorts of 
dung and compost contain some matter which, when 
mixed with the soil, ferments therein ; and by such fer- 
ment dissolves, crumbles, and divides the earth very 
much. This is the chief and almost only use of dung." 



INTRODUCTION 9 

While underestimating the value of manure, he has 
shown the importance of thorough tillage of the soil 
more clearly than had ever been done before. " The 
Horse-Hoeing Husbandry" by Jethro Tull is worthy 
of careful study by all agricultural students. 

During recent years the agricultural experiment 
stations of this and other countries have made soils a 
prominent feature of their work. Some of the results 
obtained are noted in the following chapters. Our 
knowledge regarding the chemistry, physics, geology, 
and bacteriology of soils is still far from complete, 
but many facts have been discovered which are of the 
greatest value to the practical farmer. The literature 
relating to soils and fertilizers has become very exten- 
sive, and in the classification of agricultural subjects 
for study, the soil forms one of the main divisions of 
agronomy. 

In soil investigations it has frequently happened, 
owing to imperfect interpretation of results and to 
the presence of many modifying influences, that the 
conclusions of one investigator appear to be directly 
contradictory to those of another. This is well illus- 
trated in the investigations relating to the assimilation 
of free atmospheric nitrogen, where seemingly opposite 
conclusions now form a complete theory. 

A scientific study of soils is valuable from an educa- 
tional point of view, as well as because the practical 
knowledge obtained can be utilized in the production 
of crops. In the cultivation of soils, complicated physi- 



lO SOILS AND FERTILIZERS 

cal, bacteriological, and chemical changes occur, many 
of which are only imperfectly understood. The fun- 
damental principles of soil fertility are, however, rea- 
sonably well estabhshed, and it is now possible to 
intelligently conserve the fertihty of soils and to pro- 
duce maximum yields of crops. Since the soil wealth 
is the greatest and the most important form of wealth 
of a nation, intelligent effort should be made for its 
conservation and development. 



CHAPTER I 
PHYSICAL PROPERTIES OF SOILS 

1. Soil. — Soil is that portion of the earth's crust 
in which plants may grow. It is composed of pulver- 
ized and disintegrated rock mixed with animal and 
vegetable matter. The rock particles are of different 
kinds and sizes, and are in various stages of decomposi- 
tion. If two soils are produced from the same kind of 
rock and differ only in the size of the particles, the 
difference is merely a physical one. If, however, one 
soil is formed largely from sandstone, while the other is 
formed from granite, and the soil particles are not the 
same in size, the difference is -both physical and chemi- 
cal. Soils are derived from different kinds of rock 
fragments, which are composed of minerals having 
a different combination of elements and different per- 
centage composition, and hence it is they differ both 
physically and chemically. It is difficult to consider 
the physical properties without also considering the 
chemical properties. The chemical and physical prop- 
erties, together, determine largely the agricultural value 
of a soil. 



12 SOILS AND FERTILIZERS 

2. Physical Properties Defined. — The physical prpp- 
erties of a soil are : 

1. Weight and volume. 

2. Size, form, and arrangement of the soil particles. 

3. The relation of the soil to air, water, heat, and 
cold. 

4. Color. 

5. Odor and taste. 

6. The relation of the soil to electricity. 

3. Weight and Volume. — Soils vary in weight with the 
composition and size of the particles. Fine sandy soils 
weigh heaviest, while peaty soils are the lightest. 
But when saturated with water, a cubic foot of peaty 
soil weighs more than a cubic foot of sandy soil. A 
given volume of clay soil weighs less than the same 
volume of sandy soil. The larger the amount of or- 
ganic matter, the less the weight. Pasture land, for 
example, weighs less than arable land. A cubic foot 
of soil from a field which has been well cultivated 
weighs less than that from a field where the soil has 
been compacted. Weight is an important property to 
consider when the total amounts of plant food in two 
soils are compared. A peaty soil containing i per cent 
of nitrogen and weighing 30 pounds per cubic foot has 
less total nitrogen than a soil containing 0.40 per cent 
of nitrogen and weighing 80 pounds. 

The weight of soils per cubic foot as determined from 
apparent density is approximately as follows : ^ 



PHYSICAL PROPERTIES OF SOILS 1 3 



Pounds 



Clay soil .... 
Fine sandy soil 
Loam soil .... 
Peaty soil .... 
Average prairie soil 
Uncultivated prairie soil 



70 to 75 
95 to no 
75 to 90 
25 to 40 

75 

65 



It is estimated that an acre of soil to the depth of 
one foot weighs in round numbers from 2,500,000 to 
4,200,000 pounds, depending upon the chemical com- 
position, size of soil particles, and state of compac- 
tion. 

The weight per cubic foot of soils in situ generally 
exceeds the weight derived from the apparent density 
of the dry soil ; this is because of the tendency of soils 
in the field to become compacted. While a dry clay 
soil reduced to a powder may show an apparent weight 
of 70 pounds per cubic foot, the field weight (air-dry 
basis) may range from 80 to 98 pounds, depending upon 
the degree of compactness. 

Between the soil particles are non-capillary or pore 
spaces occupied by air or water. If the soil be con- 
sidered a homogeneous mass without air spaces, it will 
have an absolute specific gravity of about 2.6 ; with the 
air spaces its apparent specific gravity is about 1.2. 
That is, in its natural condition a soil weighs about 1.2 
times heavier than the same volume of water. The 
porosity of a soil is determined by dividing the apparent 



14 



SOILS AND FERTILIZERS 



by the real specific gravity.^ Ordinarily cultivated soils 
have a pore space range from 30 to 60 per cent of the 
volume of the soil, depending upon the conditions to 
which the soil has been subjected. 

4. Size of Soil Particles. — The size of soil particles 
varies from those hardly distinguishable with the micro- 
scope to coarse rock fragments and determines the type 
of a soil as sand, clay, or loam. The term ' fine earth ' 
is used to designate that part of a soil which passes 
through a sieve with holes 0.5 mm. (0.02 inch) in di- 
ameter. Coarse sand particles and rock fragments 
which fail to pass through the sieve are called skeleton. 
The amounts of fine earth and skeleton are variable. 
Arable soils, in general, contain from 5 to 20 per cent 
of skeleton. 

The fine earth is composed of six grades of soil parti- 
cles. The names and sizes are as follows : 



Medium sand 
Fine sand 
Very fine sand 
Silt . . ., 
Fine silt . . 
Clay . . . 



Millimeters 



0.5 to 0.25 
0.25 to O.I 
O.I to 0.05 
0.05 to O.OI 
o.oi to 0.005 
0.005 ^"d less 



Inches 



0.02 to O.OI 
O.OI to 0.004 
0.004 to 0.002 
0.002 to 0.OC04 
0.0004 to 0.000; 
0.0002 and less 



Soils are mechanical mixtures of various-sized par- 
ticles. In most soils there is a predominance of one 



PHYSICAL PROPERTIES OF SOILS 



15 



grade, as clay in heavy clay soils, and medium sand 
in sandy soils. No soil, however, is composed entirely 
of one grade. The clay particles are exceedingly 
small ; it would take 5000 of the larger ones, if laid in 







(p f^ t> 
9 d -» 


' i , ^ " 


a. <ii^ & ^ 





^ ^ i 
^ ^ 1 









Fig. I. Medium sand x 150. Fig. 2. Fine sand x 150. FiG. 3. Very fine 
sand X 150. Fig. 4. Silt x 325. Fig. 5. Fine silt x 325. FiG. 6. Clay x 325. 



a line with the edges touching, to measure an inch, 
while it would take but 50 of the medium sand par- 
ticles to measure an inch. 

5. Sand. — Sand is any rock fragment ranging in size 
between 0.5 and 0.05 mm. in diameter. There are 



l6 SOILS AND FERTILIZERS 

three grades, — fine, medium, and very fine. The chief 
characteristic of sand is non-cohesion of particles. A 
soil composed entirely of sand has little, if any, agri- 
cultural value. Sandy soils usually contain from 5 
to 15 per cent of clay and silt. The relative size of 
sand, silt, and clay is shown in the illustration. In the 
coarser grained sand, quartz predominates, while the 
finer grained is composed mainly of other minerals. 

6. Clay. — The term ' clay ' used physically denotes 
those soil particles less than 0.005 ™rn- (0.0002 inch) 
in diameter, without regard to chemical composition. 
It may be silica, feldspar, limestone, mica, kaolin, or 
any other rock or mineral which has been pulverized 
until the particles are less than 0.005 i^im. in diameter. 
Chemically, however, the term 'clay' is restricted to one 
material, as explained in Section 74. The physical 
properties of clay are well known. It has the power to 
absorb large amounts of water, and will remain sus- 
pended in water for a long time. The roiled appear- 
ance of many streams and lakes is due to the presence 
of suspended clay particles. The amount in agricul- 
tural soils may range from 3 to 40 per cent. Clay 
soils, if worked when too wet, become puddled; then 
percolation cannot take place, and the accumulated 
surface water must be removed by the slow process of 
evaporation. As clays dry, they shrink, become tena- 
cious, and are worked with difficulty. Clay soils owe 
their properties to the fineness of division of the par- 



PHYSICAL PROPERTIES OF SOILS 1 7 

tides rather than to their chemical composition. Any 
mineral when finely pulverized has physical properties 
similar to clay.'' 

7. Silt. — Silt is composed of a great variety of rock 
fragments. The particles are, in size, between sand 
and clay. Chemical analysis shows them to be more 
hydrated than the clay particles. Many of the western 
prairie subsoils, clay-like in nature, are composed 
mainly of silt, which imparts characteristics intermedi- 
ate to sand and clay. While a clay soil is nearly im- 
pervious to water, and when wet works with difficulty, a 
silt soil is more permeable, but is not so open and 
porous as a sandy soil. When a soil containing large 
amounts of clay and silt is treated with water, the silt 
settles slowly, while the clay remains in suspension. 
The fine deposit in ditches and drains, where the 
water moves slowly, is mainly silt. Soils composed 
largely of silt deposited by water and mixed with vege- 
table matter are among the most fertile. 

8. Form of Soil Particles. — Soil particles are ex- 
tremely varied in form. When examined with the 
microscope they show the same diversity as is observed 
among larger stones. In some soils the particles are 
spherical, while in others they are angular. The shape 
is determined by the way in which the soil has been 
formed, and also by the nature of the rock from which 
it was produced. 



1 8 SOILS AND FERTILIZERS 

The form and arrangement of the particles are im- 
portant factors to consider in deaHng with the water 
content of soils. In the wheat lands of the Red River 
Valley of the North, the particles are small and spher- 
ical, being formed largely from limestone rock, while 
the subsoil of the western prairie regions is composed 
largely of angular silt particles, intermingled with clay, 
forming a mass containing only a minimum of inter-soil 
spaces. The silt particles being angular and embedded 
in the clay, the soil has more the character of clay than 
of silt. While these two soils are unlike in physical 
composition, the form and arrangement of the particles 
give each nearly the same water-holding power. Two 
soils may have a somewhat similar mechanical composi- 
tion and yet possess materially different physical proper- 
ties because of a difference in the form and arrangement 
of the soil particles. In some soils lo per cent of clay 
is of more agricultural value than in other soils. Ten 
per cent of clay associated with 60 or 70 per cent of 
silt makes a good grain soil, while 10 per cent of clay 
associated largely with sand makes a soil poorly suited 
to grain culture. 

The classification of the soil particles into clay, silt, 
and fine, medium, and coarse sand is purely an arbitrary 
one. Various authors use these terms in different ways, 
and when comparing the mechanical composition of soils 
reported in different works, one may avoid confusion 
by omitting the names and noting only the sizes of the 
particles. 



PHYSICAL PROPERTIES OF SOILS I9 

9. Number of Particles per Gram of Soil. — It has 

been estimated that a gram of productive soil contains 
from 2,000,000,000 to 20,000,000,000 soil particles ; soils 
which contain less than 1,700,000,000 are unproduc- 
tive. The number of particles in a given volume of 
soil varies with their size and form. According to 
Whitney^ the number of particles per gram of differ- 
ent soil types is as follows : 

Early truck 1,955,000,000* 

Truck and small fruit ...... 3,955,000,000 

Tobacco 6,786,000,000 

Wheat ........ 10,228,000,000 

Grass and wheat 14,735,000,000 

Limestone ........ 19,638,000,000 

Assuming the particles are all spheres, it is es- 
timated that in a cubic foot of soil a surface area of 
from two to three and one half acres is presented to 
the action of plant roots. 

10. Method employed in Separating Soil Particles. — 

Sieves with circular holes 0.5, 0.25, and o. i mm. are 
employed for the purpose of separating the coarser 
grades of sand. The sieve a, 0.5 mm, size, is connected 
with the filtering flask c by means of the tube b, and the 
flask is connected at point d with a suction pump. Ten 
grams of soil, after soft pestling with boihng water, are 
placed in the sieve and water is passed through until the 
washings are clear. All particles larger than 0.5 mm. 
* Figures below sixth place omitted and ciphers substituted. 



20 



SOILS AND FERTILIZERS 



remain in the sieve, and after drying and igniting, are 
weighed. The contents of the flask c, containing the 
particles less than 0.5 mm., are now passed through a 
sieve having holes 0.25 mm. in diameter. 

The fine sand and silt are separated by gravity. The 
fine sand with some silt and clay are read- 
ily deposited and the water containing the 
suspended clay is decanted into a second 
glass vessel. The residue is treated with 
more water and allowed to settle, this opera- 
tion being repeated until the microscope 
shows the soil particles to be nearly all 
of one grade. The separation of silt 
and clay is facilitated 
by the use of a centri- 
fuge.^ 

It is often difficult to fig. 8. 

secure even an approximate separation of sand, silt, and 
clay particles, because the finer particles tenaciously ad- 
here to the larger ones. 

The clay is obtained by evaporating an aliquot por- 
tion of the washings or by determining the total per 
cent of the other grades of particles and the volatile 
matter and subtracting the sum from 100. This is the 
modified Osborne sedimentation method.^'' 

By means of Hilgard's elutriator^ a more extended sep- 
aration of the soil particles is effected. For detailed direc- 
tions for making mechanical analyses of soils the student 
is referred to Wiley's " Agricultural Analysis," Vol. I. 





Fig. 7. 



PHYSICAL PROPERTIES OF SOILS 



21 



SOIL TYPES 

ll.\(Jrop Growth and Physical Properties. — The pref- 
erence of certain crops for particular kinds of soil, as 
wheat for a clay subsoil, potatoes for a sandy soil, and 
corn for a silt soil, is due mainly to the characteristic of 
the crop in requiring a definite amount of water, and a 
certain temperature 
for growth. These 
conditions are met 
by the soil being 
composed of various 
grades of particles 
which enable a cer- 
tain amount of water 
to be retained, and 
the soil to properly 
respond to heat and 
cold. In considering 
soil types, it should 
be remembered that 
there are so many 
conditions influenc- 
ing crop growth that 
the crop-producing 
power cannot always be determined by a mechanical 
analysis of the soil. The following types have been 
found to hold true in a large number of cases under 
average conditions, but they do not represent what 




Fig. io. 



First Centrifuge used in the Mechan- 
ical Analysis of Soils. 



22 SOILS AND FERTILIZERS 

might be true under special conditions. For example, 
a sandy soil of good fertility in which the bottom water 
is only a few feet from the surface, may produce larger 
grain crops than a clay soil in which the bottom water 
is at a greater depth. In judging the character of a 
soil, the special conditions must always be taken into 
consideration. In discussing the following soil types, a 
normal supply of plant food and an average rainfall 
are assumed in all cases. ^^ 

12. Potato and Early Truck Soils. — The better types 
of potato soils are those which contain about 60 per 
cent of medium and fine sand, 30 per cent of silt, and 
about 5 per cent of clay. Soils of this nature when 
supplied with 3 per cent of organic matter will contain 
from 10 to 20 per cent of water. The best conditions 
for crop growth exist when the soil contains about 18 
per cent of water. In a sandy soil, vegetation may 
reduce the water to a much lower point than in a clay 
soil, because the sandy soil gives up its water so readily 
to growing crops and consequently a larger amount is 
available, while on a heavy clay, crops show the want of 
water when the soil contains from 10 to 12 per cent, 
for the clay holds the water so tenaciously. When 
potatoes are grown on soils where there is an abnormal 
amount of water the crop is slow in maturing. For 
early truck purposes in northern latitudes, sandy loam 
soils are the most suitable because they warm up so 
readily, and the absence of an abnormal amount of 



PHYSICAL PROPERTIES OF SOILS 23 

water results in early maturity. Excellent crops of 
potatoes are grown on many of the silt soils of the 
west which have a materially different composition from 
the type given. A soil may have all of the requisites 
physically for the production of good potato and 
truck crops, and still be unproductive on account of 
unbalanced chemical composition or lack of plant 
food. 

13. General Truck and Fruit Soils. — For fruit grow- 
ing and general truck purposes the soil should contain 
more clay and less sand than for early truck farming. 
Soils containing from lo to 15 per cent of clay and not 
more than 50 per cent of sand are best suited for grow- 
ing small fruits. Such soils will retain from 12 to 20 
per cent of water. There is a noticeable difference in 
the adaptability of different kinds of fruit to different 
soils. Some thrive on clay land, provided the proper 
cultivation and treatment are given. There is as much 
diversity of soil required for producing different fruit 
crops as for the production of different farm crops. As 
a rule, however, a silt soil is most capable of being 
adapted to the various conditions required by fruit 
crops. 

14, Corn Soils. — The strongest types of corn soils 
are those which contain from 40 to 45 per cent of 
medium and fine sand and about 15 per cent of clay. 
Corn lands should contain 15 per cent of available 



24 SOILS AND FERTILIZERS 

water. Heavy clays require more cultivation and pro- 
duce corn which matures later than that grown on soil 
not so close in texture. Many corn soils contain less 
sand and clay, but more silt than the figures given. 
If a soil has a high per cent of neutral organic matter, 
good corn crops may be produced where there is less 
than 12 per cent of clay. Soils with a high per cent 
of sand are usually too deficient in available water to 
produce a good crop of corn. On the other hand, 
heavy clay soils are slow in warming up and thus are 
not suited to corn culture. The western prairie soils, 
which produce most of the corn raised in the United 
States, are composed largely of silt. 

The best types of corn soils have the necessary 
mechanical composition for the production of good crops 
of sorghum, cotton, flax, and sugar beets. However, 
the amount of available plant food required for each of 
these crops is not the same. 

15. Medium Grass and Grain Soils. — For the produc- 
tion of grass and grain a larger amount of water is 
required than for corn. The yield is determined largely 
by the amount of water which the soil contains. For 
an average rainfall of 30 inches, a good grass and grain 
soil should contain about 15 per cent of clay and 60 per 
cent of silt. Such a soil ordinarily holds from 18 to 25 
per cent of water. Many grass and grain soils have less 
silt and more clay. A soil composed of about 30 per 
cent each of fine sand, silt, and clay, is also suitable 



PHYSICAL PROPERTIES OF SOILS 



25 



mechanically, for general grain production. There are 
a number of different types of grass and grain soils, 
with different proportional amounts of sand, silt, and 



Clay 




f 


I^^Pl 


Fine ! 


'•'''•'•'"•'■'••{'•':: 


Silt 1 


(I:--' :■.':'■ '-l'^ 


Silt i 




I 
Very | 




Fina -; 


^^^osScK 


Sand L 


^^^ES*' 









o«2oo'ooeoo 



t^.. -m 






Fig. ir. Soil Types. 

I. Heavy wheat soil. 2. Average wheat soil. 3. Medium wheat and grain 

soil. 4. Corn soil. 

clay. Silt soils, however, form the largest part of the 
grain soils of the United States. 



16. Wheat Soils. — For wheat production, soils of 
closer texture are required than for other small grains. 
There are three classes of wheat soils. In the first 



26 SOILS AND FERTILIZERS 

(i in Fig. ii) there are from 30 to 50 per cent of clay 
particles, mostly disintegrated limestone. The soil of 
the Red River Valley of the North belongs to this class. 
The surface soil contains from 7 to 10 per cent of 
vegetable matter and the subsoil about 25 per cent of 
limestone in a very fine state of division. For the pro- 
duction of wheat, the subsoil should have a good store 
of water. 

The second type of wheat soil (2 in Fig. 11) has less 
clay and more silt. Many prairie subsoils which pro- 
duce good crops of wheat contain about 25 per cent of 
sand, 50 per cent of silt, and from 18 to 25 per cent of 
clay. Soils of this class when well stocked with moisture 
in the spring produce good crops of wheat, but are not 
able to withstand drought so well as soils of the first 
class ; during wet seasons, however, the yields are larger 
than on heavier clay soils. 

To the third class of wheat soils (3 in Fig. 11) belong 
those which are composed mainly of silt, containing 
usually 75 per cent, and from 10 to 15 per cent of 
clay. The high per cent of fine silt gives the soil clay- 
like properties. Soils of this class are adapted to a 
great variety of crops. For the production of wheat it 
is essential that a good supply of organic matter be 
maintained in such soils so as to bind together the soil 
particles. The special peculiarities of the different 
grain crops as to soil requirements are discussed in 
connection with the food of crops. 



PHYSICAL PROPERTIES OF SOILS 



27 



Mechanical Composition of Soil Types ^ 



Kind of Soil 


Heavy 
Wheat 


Medium 
Wheat 


Grass 

and 

Grain 


Corn 


Potato, 

ETC. 


Name of Particles 


Size in Millim. 


1 


2 


3 


4 


5 


Medium sand 


0.5 to 0.25 




3.18 


1.20 


24.60 


59.04 


Fine and very 














fine sand 


0.25 to 0.05 


6.18 


21.43 


4.14 


21.51 


5.60 


Silt 


0.05 to O.OI 


20.25 


27.75 


44-35 


11.08 


9.07 


Fine silt 


o.oi to 0.005 


IO-35 


17.60 


3075 


12.81 


19-33 


Clay 


0.005 


57.00 


25.00 


15-45 


22.80 


4.05 


Total volatile 




6.22 


5.04 


4.11 


7.20 


2.91 



1. A heavy wheat soil from the Red River Valley, — the clay 
consists largely of disintegrated limestone. 

2. Medium wheat soil from Western Minnesota. 

3. A loam soil adapted to grasses and grains. From Minnesota 
Experiment Station. 

4. A corn soil from Southwestern Minnesota. 

5. A potato soil from Eastern Minnesota. 



17. Sandy, Clay, and Loam Soils. — Ordinarily in 
agricultural literature, the term 'sandy,' 'clay,' or 'loam' 
is used to designate the prevaihng character of a 
soil. Sandy soils usually contain 90 per cent or more 
of silica or chemically pure sand. The term ' light 
sandy soil ' is sometimes used to indicate that the 
soil is easily worked, while ' heavy clay ' means that 
the soil offers great resistance to cultivation. Many 
soils which are clay-like in character are not composed 



28 



SOILS AND FERTILIZERS 



very largely of clay. There are subsoils in the western 
states which have clay-like characteristics but contain 
only about 15 per cent of clay, the larger part of the 
soil being silt. A loam soil is a mixture of sand and 
clay ; if clay predominates, it is a clay loam, while if 
sand predominates, it is a sandy loam. 

RELATION OF THE SOIL TO WATER AND AIR 

18. Amount of Water required by Crops. — Experi- 
ments show that it takes from 275 to 375 pounds of 
water to produce a pound of dry matter in a grain crop. 
In order to produce an acre of average wheat, 350 tons 
of water are needed. The amount of water required 
for the production of an acre of various crops is as 
follows : ^^ 



Clover . 
Potatoes 
Wheat . . 
Oats . . . 
Peas 

Corn . . . 
Grapes . 
Sunflowers" 



Average Amount 
Tons Water 



400 
400 

375 
375 
300 

375 
6000 



Minimum Amount 
Tons Water 



310 

325 
300 
300 
300 



The amount of water required for the production of 
crops in humid and arid regions has not been exten- 



PHYSICAL PROPERTIES OF SOILS 29 

sively investigated. Ordinarily crop yield is directly 
proportional to and dependent upon the water supply. 
The rainfall during the time of growth is frequently 
less than the amount of water required for the produc- 
tion of the crop. One inch of rainfall is equal to about 
112 tons of water per acre. An average of two inches 
per month during the three months of crop growth is 
equivalent to only 675 tons, a large part of which is lost 
by surface drainage and by evaporation. Hence it is 
that the rainfall during an average growing season is 
less than the amount of water required to produce 
crops, and consequently the water stored up in the 
subsoil must be drawn upon to a considerable extent. 
Inasmuch as the soil's reserve supply of water is such 
an important factor in crop production, it follows that 
the capacity of the subsoil for storing up and supplying 
water as needed is a matter of much importance, par- 
ticularly since the power of the soil for absorbing and 
retaining water may be influenced by cultivation and 
manuring. Before discussing the influence of cultiva- 
tion upon the soil water, the forms in which water is 
in the soil should be studied. It is present in three 
forms: (i) bottom water, (2) capillary water, and (3) 
hydroscopic water. 

19. Bottom Water is that which stands in the soil at 
a general level, and fills all the spaces between the soil 
particles. Its distance from the surface can be told in 
a general way by the depth of surface wells. Bottom 



30 SOILS AND FERTILIZERS 

water is of service to growing crops when it is at such 
a depth that it can be brought to the plant roots by 
capillarity, but when too near the surface, so that the 
roots are immersed, the conditions are unfavorable for 
crop growth. When the bottom water can be brought 
within reach of the roots by capillarity, a crop has an 
almost inexhaustible supply. In many soils known as 
old lake bottoms, such a condition exists. 

20. Capillary Water. — The water held in the minute 
spaces above the bottom water is known as the capillary 

water. The capillary spaces 
of the soil are the small spaces 
between the soil particles in 
which water is held by surface 
tension, the force acting be- 
tween the soil and the water 
Fig. 12. Water Film surrounding being greater than the force 
Soil Particles. q£ gj-^vity. If a scrics of glass 

tubes of different diameters be placed in water, it will be 
observed that in the smaller tubes water rises much 
higher than in the larger. The water rises in all of 
the tubes until a point is reached where the force of 
gravity is equal to the force of surface tension. In 
the smaller tubes surface tension is greater than the 
force of gravity, and the water is drawn up into the 
tube inversely proportional to its diameter. In the 
larger tubes the surface tension is less and the water 
is raised only a short distance. There are present in the 




PHYSICAL PROPERTIES OF SOILS 



31 



soil many spaces which are capable of taking up water 
in the same way. The height to which water can be 
raised by capillarity de- 
pends upon the size and 
arrangement of the soil 
particles, it may be to a 
height of several feet. 
Ordinarily, however, the 
capillary action of water 
is confined to a few feet. 
The arrangement of the 
soil particles influences 
greatly the capillary power 
of a soil. Usually from 
30 to 60 per cent of the 
bulk of a soil is air space ; 
by compacting, the air 
spaces are decreased ; by 
stirring, they are increased. 
In soils of close texture, 
as heavy clays, an increase 
in air spaces results in an 
increase of capillary spaces 




Fig. 13. Showing Rise of Water in 
Capillary and other Tubes. 



and of water-holding capacity, while in other soils, as 
coarse sandy soils, increasing the air spaces decreases 
the capillary spaces and the water-holding capacity. 
The best conditions for crop production exist when the 
soil contains water to the extent of about 40 per cent 
of its total capacity for saturation. 



32 SOILS AND FERTILIZERS 

21. Hydroscopic Water. — By hydroscopic water is 
meant the water that is held mechanically in the soil 
and is not removed by air drying. The air which 
occupies the non-capillary spaces of the soil is charged 
with moisture in proportion to the water in the soil. 
Under normal conditions the soil atmosphere is nearly 
saturated. When soils have exhausted their capillary 
water, the water in the soil atmosphere is correspond- 
ingly reduced. The available supply in other forms 
being exhausted, the hydroscopic, water cannot con- 
tribute to plant growth unless supplemented by heavy 
fogs. 

22. Loss of Water by Percolation. — Whenever a 
soil becomes saturated, percolation or a downward 
movement of the water begins. The extent to which 
losses by percolation may occur depends upon the 
character of the soil and the amount of rainfall. 
When soils are covered with vegetation, the losses 
are less than from barren fields. In all soils which 
have only a limited number of capillary spaces and a 
large number of non-capillary spaces, the amount of 
water which can be held above the bottom water is 
small. From such soils the losses by percolation are 
greater than from soils which have a larger number 
of capillary spaces, and a smaller number of non-capil- 
lary spaces. In coarse sandy soils many of the spaces 
are too large to be capillary. 

If all of the water which falls on some soils could 



PHYSICAL PROPERTIES OF SOILS 33 

be retained and not carried beyond the reach of crops 
by percolation, there would be an ample supply for 
agricultural purposes. The texture of the soil may be 
changed by cultivation and by the use of manures so 
as to prevent losses by percolation. If the soil is of 
very fine texture, as a heavy clay, percolation is slow, 
and before the water has time to sink into the soil, 
evaporation takes place. With good cultivation, the 
water is able to penetrate to a depth beyond the im- 
mediate influence of evaporation. Compacting an open 
porous soil by rolling, checks rapid percolation and pre- 
vents the water from being carried beyond the reach of 
plant roots. Thus it will be seen that the treatment 
necessary to prevent excessive losses by percolation, 
varies with different soils. In regions of heavy rain- 
fall and mild winters the losses of both water and plant 
food by percolation are often large, 

23. Loss of Water by Evaporation, — The factors 
which influence evaporation are temperature, humidity, 
and rate of movement of the air. When the air con- 
tains but little moisture and is heated and moving 
rapidly, the most favorable conditions for evaporation 
exist. In semi-arid regions the losses of water by 
evaporation are much greater than by percolation. 
The dry air comes in contact with the soil, the soil 
atmosphere gives up its water taken from the soil, 
and, unless checked by cultivation, the subsoil water is 
brought to the surface by capillarity and lost. In porous 

D 



34 SOILS AND FERTILIZERS 

soils a greater freedom of movement of the air is possi- 
ble, which increases the rate of evaporation. When the 
surface of the soil is covered with a layer of finely pul- 
verized earth, or with a mulch, excessive losses by 
evaporation cannot take place, because a material of 
different texture is interposed between the soil and the 
air. 

24. Loss of Water by Transpiration. — Losses of 
water may also occur from the leaves of plants by 
the process known as transpiration. Helriegel ob- 
served that during some years lOO pounds more water 
were required to produce a pound of dry matter than in 
other years, because of the difference in the amount of 
water lost in this way. The loss of water by evapora- 
tion can be controlled by cultivation, but the loss by 
transpiration can be only indirectly influenced. Hot, 
dry winds may cause crops to wilt because the water 
lost by transpiration exceeds the amount which the 
plant takes from the soil. 

25. Drainage. — Good drainage is essential in order 
to properly regulate the water supply. An excess of 
water in the soil is equally as injurious as a scant 
amount. If the water which falls on the land is allowed 
to flow over the surface and is not retained in the soil, 
there is not sufficient reserve water for crop growth. 
The object of good drainage is to store as much water 
as possible in the subsoil and prevent surface accumu- 



PHYSICAL PROPERTIES OF SOILS 35 

lation and loss. Good drainage is accomplished by 
thorough cultivation, and in regions of heavy rainfall, 
by tile drainage. Well-drained land is warmer in the 
spring, has a larger reserve store of water, and is in 
better condition for crop growth. Many swampy lands 
are highly productive when properly drained. A high 
state of productiveness cannot be maintained without 
suitable provision for drainage. When the pores of the 
soil are filled with water, air is excluded and the neces- 
sary chemical and bacteriological changes which result 
in rendering plant food available fail to take place. The 
drainage of wet and low lands forms an important fea- 
ture of rural engineering. 

26. Influence of Forest Regions. — The deforesting of 
large areas near the sources of rivers has an injurious 
influence upon the moisture content of adjoining farm 
lands. By cutting over and leaving barren large tracts, 
less water is retained in the soil. Also near forests the 
air has a higher moisture content, due to the water given 
off by evaporation. Lands adjacent to deforested dis- 
tricts lose water more rapidly by evaporation, because 
the air is so much drier. In Section 24 it is stated that 
losses of water by transpiration can be indirectly influ- 
enced. This can be accomplished by retaining the 
forests. 

Good drainage is necessary not only for individual 
farms, but also for an entire community. Good storage 
capacity in the form of forest lands, for the surplus 



36 SOILS AND FERTILIZERS 

water which accumulates near the sources of large 
rivers is also a necessity to agriculture. 

The three ways by which crops are deprived of water 
are, — (i) percolation, (2) evaporation, and (3) transpira- 
tion. With proper methods of cultivation losses by per- 
colation and evaporation may be controlled, and losses 
by transpiration may be reduced. 

INFLUENCE OF CULTIVATION UPON THE WATER 
SUPPLY OF CROPS 

27. Capillarity influenced by Cultivation. — The capil- 
larity and moisture content of soils can be influenced by 
__ different methods of 

"^"^-^S^^^^^^,^^ cultivation, as rolling 

and subsoiling, deep 
plowing, and shallow 
surface cultivation. 
lilllilllUliJilliiiiJilliJiliJIIillllllliiyi!::^^ uJi^iM^^ Xhe treatment which 

FIG. 15. Soil with Surface Cultivation. ^ ^^-j ^^^^^^^ rCCCive 

in order to insure the best water supply for crops must 
vary with the rainfall, the nature of the soil, and the 
crop to be produced. It frequently happens that the 
annual rainfall is sufficient to produce good crops, but it 
is too unevenly distributed, and hence is not all utilized 
to the best advantage. Losses of water occur through 
surface drainage, percolation, and excessive evaporation, 
but if it were properly stored in the subsoil and conserved 
by cultivation, these losses would be prevented and there 
would be sufficient for crop production. 





PHYSICAL PROPERTIES OF SOILS 37 

It is possible, to a great extent, to vary the cultiva- 
tion so as to conserve the moisture of the soil to meet 
the requirements of crops. 

28. Shallow Surface Cultivation. — When shallow sur- 
face cultivation is practiced, the capillary spaces near 
the surface are destroyed and the direct connection of 
the subsoil water with 




l||iiiii,iilllFlllJliii|lll.lfi|ftiitii 

the upper layer is If 
broken, the ground is 
covered with finely 

pulverized earth, and ^^' ■ — — — ——^-^.^ \ j 

the soil particles have ^'^- ^^- s°'' ^■''^^°"* ^""^^^^ Cultivation. 
been disturbed so there is not that close contact which 
enables the water to pass from particle to particle. When 
evaporation takes place there is a movement of the sub- 
soil water to the surface, but if that is covered with a 
layer of fine earth, the subsoil water cannot readily pass 
through such a medium, and evaporation is checked. 
Hence shallow surface cultivation conserves the soil 
moisture. 

The means bv which surface cultivation is accom- 
plished must, of necessity, vary with the nature of the 
soil. If a harrow is used, the pulverization should be 
complete, if a disk, the teeth should be set at an angle, 
and not perpendicularly, so as to prevent, as suggested 
by King,^^ the formation of hard ridges which hasten 
evaporation. When the disk is set at an angle, a layer 
of soil is completely cut off, and the capillary connec- 



38 



SOILS AND FERTILIZERS 



tion with the subsoil is broken. Surface cultivation 
should be from two to three inches deep, and the finer 
the condition in which the surface soil is left, the better. 
Shallow surface cultivation does not mean that the soil 
should not be previously well prepared by thorough cul- 
tivation. It can be practiced in connection with deep 
plowing, shallow plowing, subsoiling, or rolling ; in fact, 
it can be combined with any method of treating the 
land, and is an effectual means of conserving soil mois- 
ture. The following example shows the extent to which 
shallow surface cultivation may conserve the soil water : ^^ 







Per Cent of Water in Cornfield 




With shallow surface 
cultivation 


Without shallow surface 
cultivation 


Soil, depth 3 to 9 inches 
Soil, depth 9 to 15 inches 


14.12 
17.21 


8.02 
12.38 



29. Cultivation after a Rain. — When evaporation 
takes place immediately after a rain, not only is there 
a loss of the water which has fallen, but there may 
also be a loss of the subsoil water by translocation, if 
nothing be done to prevent.^^ After a rain, soils should 
be cultivated as soon as the implements will work well, 
so as to check evaporation and prevent the formation 
of a crust. The following example shows the extent 
to which the subsoil water may be brought to the 
surface : ^* 



PHYSICAL PROPERTIES OF SOILS 



39 





Per Cent of W;»ter 




Surface soil. 
I to 3 inches 


Subsoil, 
6 to 12 inches 


Before the shower 

After the shower 


9-77 

22.11 


18.22 
16.70 



The rainfall was sufficient to have raised the water 
content of the surface soil to 20.77 P^r cent. The sub- 
soil showed a loss of 1.52 per cent, while the surface 
soil showed a gain of 1.34 per cent in addition to the 
water received from the shower. If evaporation begins 
before the equilibrium is reestablished, there is lost, not 
only the water from the shower, but also the water 
which has been translocated from the subsoil to the 
surface. Hence the importance of shallow surface 
cultivation immediately after a rain. 

When the subsoil contains a liberal supply of water, 
and the surface soil a minimum amount, there is after a 
shower a movement of the subsoil water to the surface. 
The soil particles at the surface are surrounded with 
films of water which thicken at the expense of the sub- 
soil water. Surface tension is the cause of this movement 
of the water to the surface, and under the conditions 
stated it is temporarily greater than the force of gravity. 

A hard, thin crust should never be allowed to form 
after a rain, because it hastens losses by evaporation, 
while a soil mulch formed by surface cultivation has the 
opposite effect. 



40 SOILS AND FERTILIZERS 

30. Rolling. — The use of heavy rollers for compact- 
ing the soil is beneficial in a dry season on a soil con- 
taining large proportions of sand and silt. Rolling 
compacts the land and improves the capillary condi- 
tion, enabhng more of the subsoil water to be brought 
to the surface. Experiments show that when land is 
rolled the amount of water in the surface soil is in- 
creased. This increase is, however, at the expense of 
the subsoil water.^^ Unless rolled land receives surface 
cultivation, excessive losses by evaporation, due to im- 
proved capillarity, may result. The use of the roller on 
heavy clay during a wet season results unfavorably. 
Occasionally, Hght rolling of clay land is beneficial in 
pulverizing the clods. 

In some localities rolling and subsequent surface cul- 
tivation are not admissible on account of drifting of the 
soil, caused by heavy winds. 

31. Subsoiling. — By subsoiling is meant pulverizing 
the soil below the furrow slice. This is accompUshed 
with the subsoil plow, which simply loosens without 
bringing the subsoil to the surface. The object of sub- 
soiling is to enable the land to retain, near the surface, 
more of the rainfall. Heavy clay lands are sometimes 
improved by occasional subsoiling, but its continued 
practice is not desirable. For orcharding and fruit 
growing, it is frequently resorted to, but is not bene- 
ficial on soils containing large amounts of sand and silt. 
Rolling and subsoiling are directly opposite in effect. 



PHYSICAL PROPERTIES OF SOILS 4 1 

Soils which are improved by rolling are not improved 
by subsoiling. The additional expense involved should 
be considered when subsoiling is to be resorted to. Ex- 
periments have not as yet been sufficiently decisive to indi- 
cate all of the conditions most favorable for this practice. 

32. Fall Plowing followed by surface cultivation con- 
serves the soil water, by checking evaporation and leav- 
ing the land in better condition to retain moisture. If 
conditions allow, fall plowing can be followed by surface 
cultivation, but in some localities heavy winds prevent 
this. It is generally better to give the surface cultiva- 
tion early the following spring. Clay land should be 
left in a ridged condition when fall plowed, so as to ex- 
pose a greater surface area and to allow a better oppor- 
tunity for the water to sink into the subsoil. Evaporation 
may take place from unplowed land during the fall, and 
in the spring the soil contain appreciably less water than 
plowed land. By fall plowing it is possible to carry over 
a water balance of lOO tons or more from one year to 
the next. 

33. Spring Plowing. — When land is plowed late in 
the spring there has been a loss of water by evapora- 
tion, and the soil has not been able to store up as much 
of the rain and snow as if fall plowing had been prac- 
ticed.^^ Then, too, dry soil is plowed under and moist 
soil brought to the surface, and if surface cultivation does 
not follow, this moisture is readily lost by evaporation, 



42 



SOILS AND FERTILIZERS 



good capillary connection of the surface soil and subsoil 
is not obtained, and the furrow slice soon becomes dry. 





Per Cent of Water in" 




Fall-plowed 
land 


Spring-plowed 
land 


From 2 to 6 inches 

From 6 to I2 inches 

From 12 to 1 8 inches 


247 
26.6 
28.8 


22.4 
24.1 
26.5 


Average difference 


2.37 per cent 



Surface cultivation should immediately follow spring 
plowing. 

34. Mulching. — The use of well-rotted manure or 
straw, spread over the surface as a mulch, prevents 
evaporation. In forests the leaves form a mulch which 
is an important factor in maintaining the water supply. 
In order that a mulch be effectual, it must be com- 
pacted, — a loose pile of straw is not a mulch. In 
reclaiming lands gullied by water, mulching is very 
beneficial, also a light mulch may be used to encourage the 
growth of grass on a refractory hillside. Surface cultiva- 
tion and mulching may be advantageously combined.^* 





Per Cent of Water in 




Mulched straw- 
berry patch 


Unmulched 


Soil 2 to 5 inches 

Soil 6 to 12 inches 

Soil 12 to 18 inches 


18.12 
22.18 
24.31 


II. 17 
18.14 
21. II 



PHYSICAL PROPERTIES OF SOILS 43 

35. Depth of Plowing. — The depth to which a soil 
should be plowed in order to give the best results must, 
of necessity, vary with the conditions. Deep plowing 
of sandy land is not advisable, particularly in the spring. 
On clay land deeper plowing should be the rule. The 
longer a soil is cultivated, the deeper and more thorough 
should be the cultivation. While shallow plowing is 
admissible on new prairie land, deeper cultivation 
should be practiced when the land has been cropped 
for a series of years. Also, the depth of plowing should 
be regulated by the season. In prairie regions, and in 
the northwestern part of the United States, shallow 
plowing is more generally practiced than in the eastern 
states. Deep plowing in the fall gives better results 
than in the spring. It is not a wise plan to plow to the 
same depth every year. Professor Roberts says : ^^ " If 
plowing is continued at one depth for several seasons, 
the pressure of the implement and the trampling of the 
horses in time solidify the bottom of the furrow, but if 
the plowing is shallow in the spring and deep in sum- 
mer and fall, the objectionable hardpan will be largely 
prevented." 

In regions of scant rainfall deep plowing of silt 
soils should be done only at intervals of three or 
five years, but with an average rainfall, deep plowing 
should be the rule on soils of close texture. The 
depth of plowing should be varied to meet the re- 
quirements of the crop and soil and the amount of 
rainfall. 



44 



SOILS AND FERTILIZERS 



36. Permeability of Soils. — The rapidity with which 
water sinks into the soil after a rain depends upon 
the nature of the soil, and the cultivation which it has 
received. Shallow surface cultivation leaves the soil in 
good condition to absorb water. When the surface is hard 
and dry a large per cent of the water which falls on roll- 
ing land is lost by surface drainage. Soils of close tex- 
ture, which contain but few non-capillary spaces, offer the 
greatest resistance to the downward movement of water. 
A soil is permeable when it is of such a texture that 

it does not allow the 
water to accumulate 
and clog the non-capil- 
lary spaces. Cultiva- 
tion may change the 
tilth of even a clay soil 
to such an extent as to 
render it permeable. 
Deep plowing increases 
permeability. In regions of heavy rains, increased 
permeability is very desirable for good crop production 
on heavy clays. Sandy and loamy soils have naturally 
a high degree of permeability, and it is not necessary 
that it should be increased. 




Fig. 17. Sandy Soil without Manure. 



37. Fertilizers. — When water contains dissolved 
salts, it is more susceptible to the influence of surface 
tension, and is more readily brought to the surface of the 
soil. In commercial fertilizers soluble salts are present. 



PHYSICAL PROPERTIES OF SOILS 



45 



However, the beneficial effect of these upon the moisture 
content of soils is liable to be overestimated, because 
the fertilizer undergoes fixation when applied, and does 
not remain in a soluble condition. Fertilizers containing 
soluble salts exercise a favorable influence upon the 
moisture content of soils, but the extent of this influence 
has never been determined under field conditions. 



38. Farm Manures. — Farm manures exercise a bene- 
ficial effect upon the moisture content of soils. When 
the manure is worked into a soil, the coarse soil particles 

and masses bind ^^.^Eiar*-"*-^ -v-.jm^ 

together, and the ^<*r.,:i!lilP' >>"■» »a*^r^^' 

non-cap il lar y 
spaces are made 
capillary. Free 
circulation of the 
air, which in- 
creases evapora- 
tion, is prevented 
when a sandy soil is manured. When soils are manured 
they retain more water, as shown by the following 
example : ^^ 




Fig. i8. Sandy Soil with Manure. 







95 PER Cent Fine 




Fine Sandy 


Sandy Soil 




Soil. 


AND 5 PER 




Per Cent 


Cent Manure. 
Per Cent 


Capacity for holding water .... 


25 


42 



46 



SOILS AND FERTILIZERS 



The manure enables the soil to retain more of the 
moisture near the surface and prevents losses by perco- 
lation. The difference in moisture content between 
manured and unmanured land is particularly noticeable 
in a dry season.^* 



Soil I to 6 inches 



Sandy Soil 

WELL Manured. 

Water 



Per Cent 
10.50 



Sandy Soil 

Unmanured. 

Water 



Per Cent 
8.10 



Coarse leached manure may have just the opposite 
effect by producing an open and porous condition of the 
soil. 

RELATION OF SOIL TO HEAT 

39. Soil Temperature. — The way in which a soil 
responds to heat and cold is an important factor in its 
crop-producing value. A soil temperature of 42° to 
50° F. is required for crop growth, and the best condi- 
tions do not exist until the soil has reached a tempera- 
ture of 60° to 70° F. During cold springs in northern 
latitudes the soil is often so cold as to retard the germi- 
nation process, and to affect the vitality of seeds, caus- 
ing a poor stand of grain. 

40. Heat required for Evaporation. — It is estimated 
that the heat required to evaporate a pound of water at 
60° F. would raise the temperature of 1000 pounds of 
water 1° F. When water evaporates, the soil is 



PHYSICAL PROPERTIES OF SOILS 47 

cooled, and if the heat for evaporation is all furnished 
by the surrounding soil, it materially lowers the soil's 
temperature and unfavorably affects crop growth. In 
the early spring, drying winds may temporarily lower 
the soil temperature by hastening evaporation. Much 
heat is unnecessarily lost in evaporating excessive 
amounts of water which should be removed by good 
systems of drainage. 

41. Temperature of Drained and Undrained Land. — 

The surface of well-drained land is usually several 
degrees warmer than that of poorly drained land. Water 
being a poor conductor of heat, it follows that soils 
which are saturated are slow to warm up in the spring. 
At a depth of 2 or 3 feet the difference in tempera- 
ture between wet and dry soils is not marked. It is to 
be observed that with proper systems of drainage the 
surplus water is removed from the surface soil and 
stored up in the subsoil for future use by the crop, and 
at the same time the temperature of the surface soil is 
raised, thus improving the conditions for growth. The 
relation of drainage to the temperature and proper 
supply of water for crop growth, receives too little con- 
sideration in field practice. When the land is well 
drained, and receives early cultivation, the conditions 
are best. 

42. Color of Soils and Absorption of Heat. — All dark- 
colored soils have greater power of absorbing heat 



48 SOILS AND FERTILIZERS 

than those light in color. Schiibler observed a differ- 
ence in temperature of 8° C. between the same soils, 
when given a white coating with magnesia and a black 
coating with lampblack.^'^ Black humus soils usually 
contain so much water that the additional heat is utilized 
for evaporation, and this results in the soil being cooler 
than light-colored sandy soil. 

43. Specific Heat of Soils. — Soils have a low specific 
heat ; it requires only about one fifth as much to raise a 
pound of soil i° as is required to raise a pound of water 
1°. When soils are wet, the specific heat is greatly 
increased, and they respond more slowly to the influ- 
ence of the sun's rays. Sand has the lowest specific 
heat of any soil constituent and retains the least water, 
hence sandy soils warm up more readily than other soils. 
On the other hand, clay soils, although slower to warm 
up in the spring, retain their heat longer. 

44. Farm Manures and Soil Temperature. — When the 
animal and vegetable matter of the soil decays, heat is 
produced. The slow oxidation of manure in the soil 
yields in the end as much heat as if the dry manure 
were burned. Whenever combustion or oxidation takes 
place, heat results. 

Manured land is usually i° or 2° warmer in the spring 
than unmanured land. It has been estimated that the 
amount of organic matter which undergoes oxidation in 
an acre of rich prairie soil produces as much heat 



PHYSICAL PROPERTIES OF SOILS 49 

annually as the burning of a ton of coal.^ The addi- 
tional heat in well-drained and well-manured land is an 
important factor in stimulating crop growth, particu- 
larly in a cold backward spring. The production of 
heat from manure is utilized in the case of hotbeds 
where manure in rotting raises the temperature of the 
soil. When soils are well manured, heat is retained 
more effectually and crops on such land often escape 
early frosts. 

45. Influence of Exposure upon Soil Temperature. — 

Land with a southern slope receives the sun's rays 
longer and at a better angle for absorbing heat than 
land sloping to the north. In valleys and low places 
the soil at night cools more rapidly than on higher 
ground, and hence crops in valleys may be injured by 
late spring and early autumn frosts, while those on 
higher and warmer land escape. 

46. Influence of Cultivation upon Soil Temperature. — 

Thorough cultivation resulting in the production of a 
fine pulverized seed bed enables the soil to absorb a 
larger amount of heat than if left in a rough lumpy con- 
dition. Cultivated land is more porous and allows 
greater freedom of movement of water into the subsoil. 
Warm spring rains have a marked effect upon the 
temperature of cultivated soils by filling the pores with 
warm water. The influence of temperature upon nitri- 
fication is discussed in Chapter IV. 



50 SOILS AND FERTILIZERS 

47. Relation of Heat to Crop Growth. — All plant life 
is directly dependent upon solar heat as the source of 
energy for the production of plant tissue. The heat of 
the sun is the main force at the plant's disposal for 
decomposing water and carbon dioxide and for produc- 
ing starch, cellulose, and other compounds. The growth 
of crops is the result of the transformation of solar heat 
into chemical energy which is stored up in the plant. 
When the plant is used for fuel or for food, the quantity 
of heat produced by complete oxidation is equal to the 
amount required for the formation of the plant's tissue. 

48. Color of Soils. — The principal materials which 
impart color to soils are organic and iron compounds. 
A union of the decaying organic matter (humus) with 
the minerals of the soil produces compounds brown or 
black in color, and consequently soils containing large 
amounts of humus are dark-colored. When moist, soils 
are darker than when dry, and soils in which the organic 
matter has been kept up by the use of manures are 
darker than unmanured soils.^^ When rich, black, prai- 
rie soils lose their organic matter through injudicious 
methods of cultivation, or when in chemical analysis it 
is extracted, the soils become light-colored. 

The red color of soils is imparted by ferric oxide ; the 
yellow, by smaller amounts of the same material. A 
greenish tinge is supposed to be due to the presence 
of ferrous compounds, such soils being so close in tex- 
ture as to prevent the oxidizing action of the air. Color 



PHYSICAL PROPERTIES OF SOILS 5 1 

may serve, to a slight extent, as an index of fertility. 
Black and yellow soils are, as a rule, the most produc- 
tive, although occasionally black soils are unproductive 
because of the presence of acid compounds injurious to 
vegetation. The main reason why black soils are so 
generally fertile is because they contain a high per cent 
of humus and nitrogen. 

49. Odor and Taste of Soils. — Soils containing liberal 
amounts of organic matter have characteristic odors due 
to the presence of aromatic bodies produced by the 
decomposition of organic matter. In cultivated soils 
these have a neutral reaction. The amount of aromatic 
compounds in soils is very small. Poorly drained peaty 
soils give off volatile acid compounds when dried. 

The taste of soils varies with the chemical composi- 
tion. Peaty soils usually have a slightly sour taste, due 
to the presence of organic acids. Alkaline, soils have 
variable tastes according to the prevailing alkaline com- 
pound. The taste of a soil frequently reveals a fault, 
as acidity or alkalinity. 

50. Power of Soils to absorb Gases. — All soils pos- 
sess, to a variable extent, the power of absorbing gases. 
When decomposing animal or vegetable matter is mixed 
with soil, the gaseous products given off are absorbed. 
Absorption is the result of both chemical and physical 
action. The chemical changes which occur, as the fixa- 
tion of ammonia, are considered in the chapter on fixa- 



52 SOILS AND FERTILIZERS 

tion. The organic matter of the soil is the principal 
agent in the physical absorption of gases ; peat has the 
power of absorbing large amounts. This action is sim- 
ilar to that of a charcoal filter in removing noxious 
gases from water, 

51. Relation of Soils to Electricity. — There is always 
a certain amount of electricity in both the soil' and the 
air. The part which it takes in plant growth is not 
well understood. The action of a strong current upon 
the soil undoubtedly results in a change in chemical 
composition, but in order to change the composition of 
the soil so as to render the unavailable plant food 
available, a current destructive to vegetation would be 
required. When plants are subjected to too strong a 
current of electricity, they wilt and have all of the after- 
effects of frost. A feeble current has either an indif- 
ferent or a slightly beneficial effect upon crop growth, 
but not sufficient to warrant its use in general crop 
production on account of cost, and it is undoubtedly 
physiological rather than chemical in its action unless 
it be in the favorable influence exerted upon nitrifica- 
tion. The electrical conductivity of soils has been taken 
by Whitney as the basis for the determination of mois- 
ture.^^ It is, however, dependent largely upon the nature 
and amount of dissolved salts. 

52. Importance of the Physical Study of Soils. — A 

study of the physical properties of soils gives much val- 



PHYSICAL PROPERTIES OF SOILS 53 

liable information regarding their probable agricultural 
value ; but while the physical properties should always 
be taken into consideration, they should not form the 
sole basis for judging the character of a soil, because 
two soils from the same locality frequently have the 
same general physical composition, although entirely 
different crop-producing power, due to differences in 
chemical composition and amounts of available plant 
food. It is not possible from a physical analysis alone 
to determine the agricultural value of a soil. 

Attempts have been made to overestimate the value 
of the physical properties of soils and to explain nearly 
all soil phenomena on the basis of soil physics, but 
important as are the physical properties, it cannot be 
said they are of more importance than the chemical or 
bacteriological. In fact, the four sciences, chemistry, 
physics, geology, and bacteriology, are all closely con- 
nected and each contributes its part to our knowledge 
of soils. 



CHAPTER II 

GEOLOGICAL FORMATION AND CLASSIFICATION OF 
SOILS 

53. Agricultural Geology. — The geological study of 
a soil concerns itself with the past history of that soil, 
the materials out of which it has been produced, together 
with the agencies which have taken part in its forma- 
tion and distribution. Geologically, soils are classified 
according to the period in the earth's history when 
formed, and also according to the agencies which have 
distributed them. The principles of soil formation and 
distribution should be understood, because of their im- 
portant bearing upon fertility. Agricultural geology 
forms a separate branch of agricultural science ; in this 
work only a few topics especially relating to soils are 
treated. 

54. Formation of Soils. — Geologists state that the 
surface of the earth was at one time soUd rock. It is 
held that soils have been formed from- rock by the 
joint action of the various agents : (i) heat and cold, 
(2) water, (3) gases, (4) micro-organisms and other forms 
of vegetable and animal life, and (5) wind. One of the 
best evidences that soil is derived from rock is that there 

54 



GEOLOGICAL STUDY OF SOILS 55 

are frequently found pieces which are rotten, and, when 
crushed, closely resemble the prevailing soil of the 
field. This is particularly true of clay soils where there 
are fragments of disintegrated feldspar that when 
crumbled are similar to the soil in which the feldspar 
was embedded. The process of soil formation is ex- 
tremely slow and the various agents have been at work 
for an almost unlimited period. 

Weathering is the joint action upon rocks of the vari- 
ous atmospheric agencies. Some rocks are more sus- 
ceptible to it than others, and in different localities even 
the same kind of rock may vary in the rapidity with 
which it responds to weathering. 

55. Action of Heat and Cold. — The cooling of the 
earth's surface, followed by a contraction in volume, 
resulted in the formation of fissures which exposed a 
larger area to the action of other agencies. The un- 
equal cooling of the rocks caused a partial separation 
of the different minerals of which the rocks were com- 
posed, resulting in the formation of smaller rock parti- 
cles from the larger rock masses. This is well illustrated 
by the familiar splitting and crumbling of stones when 
heated. Shaler estimates that a variation of 150° F. 
will make a difference of i inch in the length of a 
granite ledge 100 feet long. As a result of changes in 
temperature there is a lessening in cohesion of the rock 
particles. The action of frost also is favorable to soil 
formation. The freezing of water in rock crevices 



56 



SOILS AND FERTILIZERS 



results in breaking up the rock masses, forming smaller 
bodies. The force exerted by water when it freezes is 
sufficient to rend large rocks. 

56. Physical Action of Water. — Water acts upon soils 
both chemically and physically. It is the most impor- 





9H 






r "■" ^^ 








' ' ^ 


^ 




%t 






^^H 


f^ 






L. 


'\ 


M->^. 






.^ ,.„>''■. 


■ - 






V, 1^ 


*jSjfi 


■ 






^Mk 


A 


■Mi 




m 


'flj 




PHgpS:^^^ 


^'-.^ ^9m 



Fig. 19. Boulder split by Frost. 
(Minnesota Geological and Natural History Survey.) 

tant agent that takes a part in soil formation. The sur- 
face of rocks has been worn away by moving water and 
in many cases deep ravines and canons have been 
formed. This is called erosion. The pulverized rock, 
being carried along by the water and deposited under 
favorable conditions, forms alluvial soil. This physical 



GEOLOGICAL STUDY OF SOILS 



57 



action of water is illustrated in the workings of large 
rivers where the pulverized rock particles are deposited 
along the river and at its mouth. Large areas of the 
soil in valleys and river bottoms have been formed in 




Fig. 20. Granite Bluff shattered by Frost. 
(Minnesota Geological and Natural History Survey.) 

this way, and in most cases these soils are of high fertil- 
ity. The action of water is not alone confined to form- 
ing soils along water courses, but is equally prominent 
in the formation of soils remote from streams or lakes, 
as in the case of soils deposited by glaciers. 

57. Glacial Action. — At one time in the earth's history, 
the ice fields of polar regions covered much larger areas 



58 SOILS AND FERTILIZERS 

than at present-^*^ Changes of climate caused a recession 
of these, and resulted in the movement of large bodies 
of ice, carrying along rocks and frozen soil. The move- 
ment and pressure of the ice pulverized the rock and 
produced soil. This action is well illustrated at the 
present time where mountains rise above the snow line, 
and the ice and snow melting at the base are replaced by- 
ice and snow from farther up, moving down the side of 
the mountain and carrying along crushed stones and 
soil. King estimates that an ice sheet lo feet in depth 
exerts a pressure of 570 pounds to the square foot. The 
frozen mass contains boulders, gravel, and sand which 
act as a grinding plate upon the rocky surfaces with 
which it comes in contact.^^ The rubbing of these two 
surfaces against each other under pressure for cen- 
turies has resulted in the production of vast areas of 
drift soil. 

When the glacier receded, stranded ice masses were 
distributed over the land. These melted slowly and by 
their grinding action hollowed out places some of which 
finally became lakes. The numerous lakes at the source 
of the Mississippi River are supposed to have been 
formed by glacial action. The terminal of a glacier is 
called a moraine and is covered with large boulders 
which have not been disintegrated. The course of a 
glacier is frequently traced by the markings or scratches 
of the mass on rock ledges. In glacial soils, the rocks 
are never angular, but are smooth because of the grind- 



GEOLOGICAL STUDY OF SOILS 59 

ing action during transportation. The area of glacial 
soils in the northern portion of the United States is 
quite large. These soils are, as a rule, fertile because of 
the pulverization and mixing of a great variety of rock. 

58. Chemical Action of Water. — The chemical action 
of water is an important factor in soil formation. While 
nearly all rocks are practically insoluble in water there 
is always some material dissolved, evidenced by the fact 
that all spring water contains dissolved mineral matter. 
When charged with carbon dioxide and other gases, 
water acts as a solvent upon rocks ; it converts many 
oxides, as ferrous oxide, into hydroxides, and produces 
new compounds more soluble or readily disintegrated, 
as deposit^ of clay, which have been formed from feld- 
spar rock by the chemical and physical action of water. 
Rock decay is often dependent upon chemical change ; 
the addition of water, or hydration of the molecule, par- 
ticularly of the silicates, is one of the most important 
chemical changes. When rocks, as feldspar, disinte- 
grate, there is an addition of 12 to 14 per cent of water 
of hydration to the disintegrated products. This chem- 
ical union of water with the rock materials entirely 
changes their properties and often prepares the way 
for other chemical changes. Water takes as prominent 
a part in the decay of rocks as in the decay of vegeta- 
ble matter. Dissolved minerals produce many chemical 
changes in both rocks and soils. The chemical action 
of fertilizers, known as fixation, can take place only 



60 SOILS AND FERTILIZERS 

when the substances are in sokition. In fact, water is 
necessary for nearly all the chemical reactions in the 
soil which result in rendering plant food available. 

59. Joint Action of Air and Gases. — In the disintegra- 
tion of materials to form soil, air takes a prominent 
part. By the aid of oxygen, carbon dioxide, and other 
gases and vapors in the air, rock disintegration is has- 
tened. The action of oxygen changes the lower oxides 
to higher forms. All rock contains more or less oxygen 
in chemical combination. The carbon dioxide of the air 
under some conditions favors the formation of carbon- 
ates. The disintegrating action of air, moisture, and 
frost is illustrated in the case of building stones which 
in time crumble and form a powder. Many of the 
benefits of cultivation are due to aeration of the soil, as 
air promotes chemical changes of mineral substances 
and prepares the way for life processes in the soil. 

60. Action of Micro-organisms. — Micro-organisms, 
found on the surface and in the crevices of rocks, are 
active agents in bringing about rock decay, deriving all 
of their energy from the chemical changes which they 
induce between minerals, and obtaining their carbon 
from the air. Such organisms incorporate organic 
matter with the rock residues.^^ Certain nitrifying 
organisms can obtain their nitrogen also from the air, 
and it is believed that they have largely prepared the 
way for the production of agricultural plants, by incor- 



GEOLOGICAL STUDY OF SOILS 6l 

porating the initial stores of carbon and nitrogen of the 
air with the disintegrated rock materials. 

61. Action of Vegetation. — Some of the lower forms 
of plants, as lichens, do not require soil for growth, but 
are capable of living on the bare surface of rocks, 
obtaining food from the air, and leaving a certain 
amount of vegetable matter which undergoes decay and 
is incorporated with the rock particles, preparing the 
way for higher orders of plants which take their food 
from the soil. When this vegetable matter decays, it 
enters into chemical combination with the pulverized 
rock, forming humates.^^ The disintegrating action of 
plant roots and vegetable matter upon rocks has been 
an important factor in soil formation. The action of 
vegetable remains in soil production is discussed in 
Chapter III. 

62. Earthworms. — Many soils have been greatly 
modified by the action of earthworms. The soil in 
passing through their digestive tract is ground into finer 
particles and is intimately mixed with the indigestible 
matter excreted by the worms. In the case of rich loam 
soils it is estimated that all of the particles have at 
some time passed through the digestive tract of earth- 
worms. Where they have been active, air and water 
are admitted into the soil more readily. The action of 
earthworms in soils has been extensively studied by 
Darwin. 



62 SOILS AND FERTILIZERS 

63. Wind. — Wind also has been an important factor 
in the production and modification of soils. The denud- 
ing effects of heavy wind storms are well known. 
Large areas of- wind-formed soils are found in some 
countries. Sand dunes are transported by winds, and 
often their subjugation by soil-binding plants is neces- 
sary in order to prevent encroachment upon valuable 
farm lands and inundation of villages. Soils formed by 
the action of winds are called aeolian soils. 

64. Combined Action of the Various Agents. — In the 
decay of rocks the various agents named ^ — water act- 
ing mechanically and chemically, heat and cold, air, 
micro-organisms, vegetation, earthworms, and wind — 
have acted jointly, and have produced more rapid disin- 
tegration than if each agent had acted separately. 

DISTRIBUTION OF SOILS 

65. Sedentary and Transported Soils. — The place 
which a soil occupies is not necessarily where it was 
formed ; that is, a soil may be produced in one locality 
and transported to another. Soils are either sedentary 
or transported. Sedentary soils are those which occupy 
the original position where they were formed. They 
usually have but little depth before rock surface is 
reached. The stones in such soils, except where modi- 
fied by weathering, have sharp angles because they 
have not been ground by transportation. In the south- 



GEOLOGICAL STUDY OF SOILS 



63 



ern part of the United States, east of the Mississippi 
River, there are large areas of sedentary soils as fer- 
rogenous clays in an advanced state of decay. 

Transported soils are those which have been formed 




Fig. 22. A Boulder-filled Channel. 
(Minnesota Geological and Natural History Survey.) 

in one locality and carried by various agents as gla- 
ciers, rivers, or winds to other localities, the angles of 
the stones in these soils having been ground off during 
transportation. Transported soils are divided into 
classes according to the ways in which they have been 
formed ; as drift soils produced by glaciers, alluvial soils 
by rivers and lakes, aeolian soils by winds, and colluvial 
soils formed of rocks and debris from mountain sides. 



64 SOILS AND FERTILIZERS 

In some localities volcanic soils are found. They are 
extremely varied in texture and composition; some are 
very fertile and contain liberal amounts of alkaline salts 
and phosphates, while others contain so little plant food 
that they are sterile. 

ROCKS AND MINERALS FROM WHICH SOILS ARE 
FORMED 

66. Composition of Rocks. — Rocks are composed of 
either a single mineral or of a combination of minerals. 
Most of the common minerals are definite chemical 
compounds and have a varied range in composition, 
due to the fact that one element or compound may be 
partially or entirely replaced by another. Most rocks 
from which soils have been derived contain minerals, as 
feldspar, mica, hornblende, and quartz. 

67. Quartz. ^ — -Quartz is the principal constituent of 
many rock formations. Pure quartz is silicic anhydride, 
SiOa, and a soil formed from pure quartz alone would 
be sterile. White sand is nearly pure quartz or silica. 
Silica enters into combination with many elements, 
forming a large number of minerals. Particles of quartz 
when cemented with iron compounds form sandstone 
rock. Sand is derived mainly from the decay of rocks 
containing quartz. 

68. Feldspar is composed of silica, alumina, and 
potash or soda. Lime may also be present, and replace 



GEOLOGICAL STUDY OF SOILS 6$ 

a part or nearly all of the soda. If the mineral contains 
soda as the alkaline constituent, it is known as albite, 
or if mainly potash, it is called potash feldspar or 
orthoclase. 

The members of the feldspar group are insoluble in 
acids, and before disintegration takes place are not 
capable of supplying plant food. Potash feldspar con- 
tains from 12 to 15 per cent of potash, none of which is 
of value as plant food until disintegrated. When feld- 
spar undergoes disintegration, it produces kaolin or clay. 
A soil formed from feldspar is usually well stocked with 
potash. Feldspar containing lime readily yields to the 
solvent action of water in which there is carbon dioxide. 

Orthoclase, AlKSigOg Potash feldspar 

Albite, AlNaSisOg Sodium feldspar 

69. Hornblende. — The hornblende and augite groups 
are formed by the union of magnesium, calcium, iron, 
and manganese, with silica. As a rule none of the 
members of the alkali family are present in hornblende. 
The augites are double silicates of iron, manganese, cal- 
cium, and magnesium. Quite frequently, phosphoric 
acid is in chemical combination with the iron. The 
members of this group are readily distinguished by 
their color, which is black, brown, or brownish green. 
The hornblendes which contain lime are quite readily 
decomposed when subjected to weathering and the 
action of water charged with carbon dioxide. They are 



66 SOILS AND FERTILIZERS 

mainly insoluble in acids, and do not as a rule form 
very fertile soils. 

70. Mica. — Mica is quite complex in composition, 
is an abundant mineral, and is composed of silica, iron, 
alumina, manganese, calcium, magnesium, and potas- 
sium. Mica is a polysilicate. The color may be white, 
brown, black, or bluish green, owing either to the ab- 
sence of iron, or to its presence in various amounts. 
The chief physical characteristic of the members of this 
group is the ease with which they are split into thin 
layers. It is to be observed that the mica group con- 
tains all the elements of both feldspar and hornblende. 
Mica is quite resistant to chemical change. 

Soils formed from thoroughly disintegrated mica are 
usually fertile, owing to the variety of essential elements 
present. 

71. Granite is composed of quartz, feldspar, and 
mica. It is a very hard rock and slow to disintegrate. 
The different shades of granite depend upon the pro- 
portion in which the various minerals are present. 
Inasmuch as it contains so many minerals, it usually 
follows that granite soil is fertile ; although when not com- 
pletely disintegrated or when disintegrated and leached, 
it is unproductive. Pure powdered granite before un- 
dergoing disintegration furnishes but little plant food. 
After weathering, the plant food gradually becomes 
available. Granite varies in both physical and chemi- 



GEOLOGICAL STUDY OF SOILS 6/ 

cal composition, and some disintegrates more readily 
than others. Gneiss belongs to the granite series, but 
differs from true granite in containing a large amount 
of mica. Mica schist contains a larger amount of mica 
than gneiss, 

72. Zeolites. — The zeolites are a large group of sec- 
ondary or derivative minerals formed from disintegrated 
rock. They are polysilicates containing alumina and 
members of the alkali and lime families, and all contain 
water held in chemical combination. They are partially 
soluble in dilute hydrochloric acid and belong to that class 
of compounds which are capable, to a certain extent, of 
becoming available as plant food. In color, they are white, 
gray, or red. Zeolites are quite abundant in clay and are 
an important factor in soil fertility. It is this group of 
hydrated silicates which takes such an important part in 
the process of fixation. The zeolites, when disintegrated, 
particularly by glacial action, form very fertile soils. 

73. Apatite or Phosphate Rock. — Apatite is com- 
posed mainly of phosphate of lime, Ca3(P04)2, together 
with small amounts of other compounds, as fluorides 
and chlorides. It is generally of a green or yellow 
color and is present in many soils, but is of little value 
as plant food unless associated with organic matter and 
soluble alkaline salts. 

74. Kaolin is chemically pure clay and is formed by 
the disintegration of feldspar. When feldspar is de- 



68 SOILS AND FERTILIZERS 

composed and acted upon by water, the potash is re- 
moved and water of hydration is taken up, forming the 
product kaolin, which is hydrated silicate of alumina, 
Al4(Si04)3 . HgO. Impure varieties of clay are colored 
red and yellow owing to the presence of iron and 
other impurities. Pure kaolin is white, is insoluble in 
acids, and is incapable of supplying any nourishment to 
plants. Clay soils are fertile on account of the other 
minerals and organic matter mixed with the clay and are 
usually well stocked with potash because of its incom- 
plete removal from the disintegrated feldspar. It is to 
be observed that the term ' clay ' used chemically means 
aluminum silicate, while physically it is any substance 
the particles of which are less than 0.005 i^^i- i^^ diameter. 

75. Limestone. — Limestone is present in many sec- 
ondary rocks. It is composed of calcium carbonate and 
is slowly soluble in water containing carbon dioxide. 
Extensive deposits of calcium carbonate, as limestone, 
marble, and chalk, occur in nature. It is widely dif- 
fused in soils, and is a constituent that imparts fertiUty. 
Many soils contain appreciable amounts of disintegrated 
limestone. 

76, Disintegration of Rocks and Minerals. — In ad- 
dition to the rocks and minerals which have been 
mentioned, there are many others that contribute to soil 
formation, as glauconite, a hydrated siHcate of iron ; 
alumina and potash ; limonite, a hydrated oxide of 



GEOLOGICAL STUDY OF SOILS 



69 



iron ; dolomite, a double carbonate of calcium and mag- 
nesium; serpentine, a silicate of magnesium; and gypsum 
calcium sulphate. All rocks and minerals are subject to 
disintegration and change in chemical composition and 
physical properties. The process of soil formation has 
resulted in numerous chemical and physical changes. 
These changes are still taking place, and as a result 
plant food is constantly being made available. 



Chemical Composition of Rocks" 





< 


< 
z 




29. 


^9 


< 

go 

< Ml 


a 
a 


u 

go 

u v 


a 

<9. 


Quartz . . . 
Feldspar . . 


95-100 

55-67 
46 

40-45 
40-55 
60-80 


20-29 
39 

12-37 

0-15 

10-15 














0-12 


I-IO 


I-II 








CS') 


14 


Apatite . . 
Mica 




53 




5-12 

4-5 




1-5 
















2-3 













77. Value of Geological Study of Soils. — Agricul- 
tural geology is a valuable aid in studying soil prob- 
lems, but like other sciences it is incapable alone of 
solving all the problems of soil fertility. Means have 
not yet been devised for accurately determining the 
extent of rock disintegration and the rapidity with 
which it has taken place or the degree to which dis- 



70 SOILS AND FERTILIZERS 

integrated minerals have been removed from rocks by 
leaching and other agencies. It js known that the 
rate of weathering of soils is influenced by various fac- 
tors, as origin, texture, composition, humidity and other 
climatic conditions, presence of decaying organic matter, 
micro-organisms, mechanical treatment and manipula- 
tion of the soil, fertilizers, sunlight and vegetation. 
Some of these agencies for promoting soil disintegra- 
tion are under the control of the farmer and are utilized 
by him in rendering plant food available. A knowledge 
of the origin of soils, of the minerals of which they are 
composed, and of the ways in which they have been 
distributed is of much assistance in determining their 
agricultural value. 



CHAPTER III 

THE CHEMICAL COMPOSITION OF SOILS 

78. Elements Present in Soils. — Physically consid- 
ered, a soil is composed of disintegrated rock mixed 
with animal and vegetable matter; chemically con- 
sidered, the rock particles consist of a large number of 
simple and complex compounds, each compound being 
composed of elements chemically united. Elements 
unite to form compounds, compounds to form minerals, 
minerals to form rocks, and disintegrated rock forms 
soil. When rocks decompose, the disintegration, except 
in a few cases, is never carried to the extent of liberating 
the elements, but the process ceases when the minerals 
have been broken up into compounds. While there are 
present in the crust of the earth between 6$ and 70 
elements, only about 1 5 are found in animal and plant 
bodies, and of these but 12 are known to be absolutely 
essential. Only four of the elements which are of most 
importance are at all liable to be deficient in soils. 
These four elements are : nitrogen, phosphorus, potas- 
sium, and calcium. 

79. Classification of the Elements. — The elements 
found most abundantly in soils are divided into two 
classes : 

71 



72 SOILS AND FERTILIZERS 

Acid-forming Elements Base-forming Elements 

Oxygen O Aluminum Al 

Silicon Si Potassium K 

Phosphorus P Sodium Na 

Sulphur S Calcium Ca 

Chlorine CI Magnesium Mg 

Nitrogen N Iron Fe 

Hydrogen H 

Carbon C 

Boron, fluorine, manganese, and barium are usually 
present in small amounts, besides others which may be 
found in traces, as the rare elements lithium and 
titanium. 

For crop purposes the elements of the soil may be 
divided into three classes : 

1. Essential elements most liable to be deficient; 
nitrogen, potassium, phosphorus, and calcium. 

2. Essential elements usually abundant ; iron, mag- 
nesium, and sulphur. 

3. Unnecessary and accidental elements, usually 
abundant; as chlorine, silicon, aluminum, and man- 
ganese. 

80. Combination of Elements. — In dealing with the 
composition of soils, the percentage amounts of the 
individual elements are not given, except m the case of 
nitrogen, but instead, the amounts of the correspond- 
ing oxides. The elements do not exist in a free state 
in soils, but are combined with oxygen and other 
elements to form compounds. When considered as 



THE CHEMICAL COMPOSITION OF SOILS 



73 



oxides, the acid and basic constituents may form various 
compounds as : 



Calcium 



Potassium 
Sodium . 
Magnesium 
Iron . . 




Silicate 

Phosphate 

Chloride 

Sulphate 

Carbonate 



The following reactions will explain some of the more 
elementary combinations : 



CaO + SiOa = CaSiOg 
3CaO + P2O5 = CagCPO^)^ 
CaO + SOg =CaS04 
CaO + CO2 = CaCOg 



CaO + N2O5 = Ca(N0g)2 

K2O + SOg 

Na20 + SOg 

MgO + SOg = MgSO^ 



K2SO, 
Na2S04 



It is often difficult to determine with accuracy the 
exact form or combination in which an element is 
present in the soil. When reported as the oxide, bases 
may be considered as combined with any of the ox- 
ides of the acid-forming elements, as indicated by 
the reactions, to form salts. Each compound of 
an element may have a different value as plant food, 
hence it is important to determine as far as possible 
the form or solubility of the various elements of plant 
food. 



74 SOILS AND FERTILIZERS 

ACID-FORMING ELEMEJ!TTS 

81. Silicon. — The element silicon makes up from 
a quarter to a third of the solid crust of the earth and 
next to oxygen is the most abundant element found in 
soils. Silicon never occurs in the soil in the free state. 
It either combines with oxygen to form silica (SiOg), or 
with oxygen and some base-forming element or elements 
to form silicates. Silica and the various silicates are 
by far the most abundant compounds present in the 
soil. Silicon is not one of the elements absolutely 
necessary for plant growth, and even if it were, all soils 
are so abundantly supplied that it would not be necessary 
to use it in fertilizers. 

When two or more base-forming elements are united 
with the siUcate radical, a double silicate results. The 
double silicates are the most common compounds 
present in soils. There are also a number of forms of 
silicic acid which greatly increase the number of sili- 
cates, and a study of the composition of soils is largely 
a study of these various silicates. 

82. Carbon is an acid-forming element and belongs to 
the same family as silicon. It is found in the soil as 
one of the main constituents of the volatile or organic 
compounds, and also unites with oxygen and the base- 
forming elements, producing carbonates, as calcium 
carbonate or limestone. The carbon of the soil takes 
no direct part in forming the carbon compounds of 



THE CHEMICAL COMPOSITION OF SOILS 75 

plants. It is not necessary to apply carbon fertilizers 
to produce the carbon compounds of plants, because 
the carbon dioxide of the air is the source for crop 
production. It is estimated that there are 30 tons 
of carbon dioxide in the air over every acre of the 
earth's surface.^ The carbon in the soil is an indirect 
element of fertility, because it is usually combined with 
other elements, as nitrogen and phosphorus, which are 
absolutely necessary for crop growth. 

83. Sulphur occurs in all soils mainly in the form of 
sulphates, as calcium sulphate, magnesium sulphate, 
and sodium sulphate. It is an essential element of 
plant food. There is generally less than o.io per cent 
of sulphuric anhydride in ordinary soils, but the amount 
required by crops is small and there is usually an 
abundance. 

84. Chlorine is found in all soils, generally in com- 
bination with sodium, as sodium chloride. It may be 
in combination with other bases. Soils which contain 
more than 0.2 per cent are, as a rule, sterile. Chlorine 
is present in the soil in soluble forms. It occurs in all 
plants but is not absolutely necessary for plant growth. 
Its use in fertilizers is unnecessary, although chlorine 
with sodium, as common salt, is sometimes used as an 
indirect fertilizer. 

85. Phosphorus, one of the essential elements for 
plant growth, is combined with both the volatile and 



^6 SOILS AND FERTILIZERS 

non-volatile elements of the soil. Plants cannot make 
use of it in other forms than the phosphates. Phos- 
phorus is usually present in the soil as calcium phos- 
phate, magnesium phosphate, or aluminum phosphate, 
and may also be combined with the humus, forming 
humic phosphates. The form of the phosphates, as 
available or unavailable, is an important factor in soil 
fertility. Soils are quite liable to be deficient in phos- 
phates, inasmuch as they are so largely drawn upon 
by many cro-ps, particularly grain crops, where the 
phosphates accumulate in the seed, and are sold from 
the farm. The phosphorus content of soils is usually 
reported as phosphorus pentoxide (P2O5), anhydrous 
phosphoric acid, commonly called phosphoric acid. 

86. Nitrogen. — This element is present in soils in 
various forms. As a mineral constituent it is combined 
with oxygen and the base-forming elements as potas- 
sium, sodium, and calcium, forming nitrates and nitrites, 
which, on account of their solubility, are never found 
in average soils in large amounts. Nitrogen is mainly 
in organic combination, being associated with carbon, 
hydrogen, and oxygen as one of the elements form- 
ing the organic matter of soils. Nitrogen may also 
be present in small amounts in the form of ammonia, or 
of ammonium salts, derived from rain water and from 
the decay of vegetable and animal matter. While free 
nitrogen is in the air in large amounts, it can be ap- 
propriated as food in this form by only a limited num- 



THE CHEMICAL COMPOSITION OF SOILS "JJ 

ber of plants and by them indirectly. For ordinary 
agricultural crops, particularly the cereals, nitrogen 
must be present in the soil as combined nitrogen. This 
is the most expensive of any of the elements of plant 
food, and is liable to be deficient. No other element 
takes such an important part in agriculture or in life 
processes as does nitrogen. 

87. Oxygen. — Oxygen is combined with both the 
acid- and base-forming elements and is found in nearly 
all of the compounds of the soil. It has been estimated 
that about one half of the crust of the earth is com- 
posed of oxygen, which in large amounts is combined 
with silicon, forming silica. That which is held in 
chemical combination in the soil takes no part in the 
formation of plant tissue. In addition to being present 
in the soil, oxygen constitutes eight ninths of the weight 
of water and about one fifth of the weight of air. It 
also forms about 50 per cent of the compounds found 
in plants and animals. Oxygen in the interstices of the 
soil is an active agent in bringing about many chemical 
changes, as oxidation of the organic matter, and disin- 
tegration of the soil particles. 

88. Hydrogen. — This element is never found in a 
free state in the soil, but is combined with carbon and 
oxygen in animal and vegetable matter, with oxygen to 
form water, and in a few cases with some of the base 
elements to form hydroxides. It is not in the soil in 



y2> SOILS AND FERTILIZERS 

large amounts, and that which forms a part of the 
tissues of plants and animals comes from the hydrogen 
in water. Hydrogen in the organic matter of soils takes 
no part directly in producing the hydrogen compounds 
of plants. On account of its lightness, hydrogen never 
makes up a very large proportion, by weight, of the 
composition of bodies. 

BASE-FORMING ELEMENTS 

89. Aluminum is present in the soil in the largest 
amount of any of the base elements. It forms probably 
from 6 to lo per cent of the solid crust of the earth. 
As previously stated aluminum is one of the constituents 
of clay, and is not necessary for plant growth. Physi- 
cally, however, the aluminum compounds take an im- 
portant part in soil fertility. Aluminum is usually in 
combination with silica or with silica and some base- 
forming element, as iron, potassium, or sodium. The 
various forms of aluminum silicate are the most numer- 
ous compounds found in soils. Alumina is the oxide of 
aluminum, AlgOg, and is the usual form in which this 
element is reported in soil and rock analyses. 

90. Potassium is in the soil mainly in the form of 
silicates, and is one of the elements absolutely necessary 
for plant growth. The term 'potash' (potassium oxide, 
K2O) is usually employed when reference is made to 
the potassium compounds. The amount and form of 



THE CHEMICAL COMPOSITION OF SOILS 79 

the soil potash have an important bearing upon fertihty. 
Potassium is one of the three elements of plant food 
usually supplied in fertilizers. The form in which it is 
in the soil and its economic supply as plant food are 
important factors in crop production. The amount of 
potash in soils ranges from 0.02 to 0.8 per cent. In a 
fertile soil it rarely falls below 0.2 per cent. 

91. Calcium is in the soil in a variety of forms, as 
calcium carbonate, calcium silicate, calcium sulphate, 
and calcium phosphate. The calcium oxide, CaO, of 
the soil is generally spoken of as the lime content. 
Calcium carbonate and sulphate are important factors 
in imparting fertility. A subsoil with a good supply of 
lime will stand heavy cropping and remain in excellent 
chemical and physical condition for crop growth. In a 
good soil there is usually 0.2 per cent or more of lime, 
mainly as calcium carbonate. 

92. Magnesium is found in all soils and is usually 
associated with calcium, forming the mineral dolomite, 
which is a double carbonate of calcium and magnesium. 
Magnesium may also be present in the soil in the form 
of magnesium sulphate or magnesium chloride. All 
crops require a certain amount of magnesia in some 
form, in order to reach maturity and produce fertile 
seeds. There is generally in all soils an amount suffi- 
cient for crop purposes, hence it is not necessary to 
consider this element in connection with fertilizers. 



80 SOILS AND FERTILIZERS 

The term 'magnesia' (magnesium oxide, MgO) is used 
when reference is made to the magnesium compounds 
of the soil. 

93. Sodium is in the soil mainly as sodium silicate, 
and to about the same extent as potassium, which it 
resembles chemically in many ways. It cannot, how- 
ever, replace potassium in plant growth. Inasmuch as 
sodium takes an indifferent part in plant nutrition, it 
is never used as a fertilizer except in an indirect way. 

94. Iron is an element necessary for plant food and is 
found in all soils to the extent of from i to 4 per cent. 
Crops require only a small amount of iron, hence there 
is always sufficient for crop purposes. Iron in soils is 
in the form of oxides, hydroxides, and silicates. 

FORMS OF PLANT FOOD 

95. Three Classes of Compounds. — For agricultural 
purposes, the compounds present in soils may be divided 
into three classes :^ ( i ) Compounds soluble in water and 
dilute organic and mineral acids ; (2) compounds soluble 
in more concentrated acids ; (3) insoluble compounds 
decomposed by strong acids and fluxes. 

96. Water- and Dilute Acid-soluble Matter of Soils. — 

This class includes silicates and other compounds of 
potash, soda, lime, magnesia, phosphorus, etc., which are 



THE CHEMICAL COMPOSITION OF SOILS 



soluble in the soil water and in very dilute organic and 
mineral acids, and represents the most soluble and the 

most active and valuable 
forms of plant food. There 
is only a very small amount 
in these forms. In loo 
pounds of arable soil, rarely 
more than 0.005 pound of 
any one of the important 
elements is soluble in the 
soil water or more than 0.05 
pound in dilute organic acids. 




97. Acid-soluble Matter of 
Soils. — The plant food of 
the second class is in a some- 
what more insoluble form, 
and consists of compounds, 
principally the zeolites, sol- 
uble in hydrochloric acid of 
23 per cent strength, sp. gr. 
I. II 5. This represents the 
limit of the solvent action 
of the roots of plants.^ In 
this class are included also 
all the mineral elements 
combined with the humus and soluble in dilute alkalies. 
As a rule, not over 10 to 20 per cent of the total soil is 
soluble in hydrochloric acid ; and the more important 



Fig. 23. Oat Plant grown in soil 
extracted with hydrochloric acid. 



82 SOILS AND FERTILIZERS 

elements make up only a small part of this amount. In 
200 samples of soil, the potash, nitrogen, lime, magnesia, 
and phosphoric and sulphuric anhydrides amounted to 
3.5 per cent ; in many fertile soils the sum of these is less 
than 1.50 per cent. This means that in every 100 pounds 
of soil there are only from 1.5 to 3.5 pounds which can 
take any active part in the support of a crop, while 96 to 
98.5 pounds are present simply as so much inert material, 
and valuable only from a physical point of view. Not 
all of the potash, for example, soluble in hydrochloric 
acid is equally valuable. In fact, the acid represents 
more than the Hmit of the crop's feeding power, when 
there is not enough of more soluble forms to aid in the 
first stages of growth. 

98. Acid-insoluble Matter of Soils. — This class in- 
cludes all of those compounds of the soil which require 
the joint action of the highest heat and the strongest 
chemicals in order to decompose them. The insoluble 
residue obtained after digesting a soil with strong hydro- 
chloric acid contains potash, soda, and limited amounts 
of magnesia and phosphoric acid, with other elements 
which are of no immediate value as plant food. When 
seed was planted in soil extracted with strong hydro- 
chloric acid, it made no growth after the reserve food in 
the seed had been exhausted. A plant grown in such 
a soil is shown in the illustration.^* (Fig- 23.) 

The acid-insoluble matter of soils is capable of under- 
going disintegration and in time may be changed to the 



THE CHEMICAL COMPOSITION OF SOILS 



83 



second or zeolitic class of silicates. This process, how- 
ever, is too slow to be relied upon as an immediate 
source of plant food. 

In the following table are given the percentage 
amounts of compounds soluble and insoluble in hydro- 
chloric acid for a few typical soils :^ 



Insoluble matter 
Potash 
Soda . 
Lime . 
Magnesia 
Iron 

Alumina 
Phosphoric acid 
Sulphuric acid 



Wheat 
Soil 



Soluble 
in HCl 



63.07 
0.54 
0.45 
2.44 
1.85 
4.18 
7.89 
0.38 
O.I I 



Insol- 
uble 
residue 



2.18 

3-55 
0.36 
0.25 
0.78 
5-54 

0.24 



Heavy Clay 
Soil 



Soluble 
inHCl 



8477 
0.21 
0.22 
0.48 
0.34 
376 
6.26 
0.12 
0.09 



Insol- 
uble 
residue 



346 
2.95 
0.16 
0.47 
0.72 

S-44 
0.08 
0.25 



Grass and 
Grain Soil 



Soluble 
inHCl 



84.08 
0.30 
0.25 
0.51 
0.26 
2.56 
2.99 
0.23 
0.08 



Insol- 
uble 
residue 



1.45 
0.25 

0-35 
0.46 
1.07 
9.72 
0.05 
0.02 



The insoluble matter, after digestion with hydro- 
chloric acid, was submitted to fusion analysis, and the 
figures given under insoluble residue represent the 
amounts of potash, soda, etc., insoluble in the acid. In 
the clay soil, 94 per cent of the total potash was in 
forms insoluble in hydrochloric acid. 



99. Soluble and Insoluble Potash and Phosphoric Acid. 

— From the preceding table it is to be observed that 



84 SOILS AND FERTILIZERS 

the larger portion of the potash in the soil is insoluble 
in hydrochloric acid. A soil may contain from 2 to 3 
per cent of total potash, and 90 per cent or more may be 
in such firm chemical combination with aluminum, sili- 
con, and other elements, as to resist the solvent action 
of plant roots. The larger portion of the phosphoric 
acid of the soil is soluble in hydrochloric acid. In some 
soils, however, from 20 to 40 per cent is present as the 
third class of compounds. When a soil is digested with 
hydrochloric acid, the insoluble residue is usually a fine 
gray powder. Some clay soils retain their red color 
even after treatment with acids, showing that the iron 
is in part in chemical combination with the more com- 
plex silicates. 

In order to decompose the insoluble residue obtained 
from the treatment with hydrochloric acid, fluxes, as 
sodium carbonate and calcium carbonate, are employed 
which, at a high temperature, act upon the complex sili- 
cates and produce silicates soluble in acids. Plants, 
however, are unable to obtain food in such complex 
forms of chemical combination. 

100. Action of Organic and Dilute Mineral Acids upon 
Soils. — Dilute organic acids, as a i per cent solution 
of citric acid, have been proposed as solvents for the 
determination of easily available plant food. It has 
been shown in the case of the Rothamsted soils which 
have produced 50 crops of grain without manure, and 
which are markedly deficient in available phosphoric 



THE CHEMICAL COMPOSITION OF SOILS 85 

acid, that a i per cent solution of citric acid dissolved 
only 0.003 per cent of phosphoric acid while the soil 
contained a total of 0.12 per cent. In the case of an 
adjoining plot which had received phosphate manures 
until the soil contained a sufficient amount of available 
phosphoric acid to produce good crops, there was pres- 
ent 0.03 per cent of phosphoric acid soluble in a i per 
cent citric acid solution. ^^ 

Dilute organic acids are, to a certain extent, capable 
of showing deficiency of plant food. A soil which 
has 0.03 per cent of potash or phosphoric acid sol- 
uble in I per cent citric acid is, as a rule, well stocked 
with these elements in available forms. Prairie soils 
of high fertility yield from 0.03 to 0.05 per cent of 
both potash and phosphoric acid soluble in dilute or- 
ganic acids ; soils which are deficient in these elements 
usually contain less than 0.0 1 per cent. 

The action of a single organic acid of specific 
strength cannot be taken as the measure of fertility 
for all soils and crops alike, because different plants 
do not have the same amount or kind of organic acid 
in the sap. Of the various organic acids, citric pos- 
sesses the greatest solvent action upon lime, magnesia, 
and phosphoric acid, while oxalic has the strongest 
solvent action upon the silicates. Tartaric acid ap- 
pears to be less active as a solvent than either citric 
or oxalic acid. The combined use of dilute organic 
acids, as citric with hydrochloric (sp. gr. 1.115), will 
generally give an accurate idea of the character of a 



86 SOILS AND FERTILIZERS 

soil. A fifth-normal solution of hydrochloric, or of 
nitric acid, has also been proposed ^ for determining 
the available plant food of soils ; a soil that yields 
less than 25 parts of phosphoric acid per million of 
soil, as soluble in fifth-normal nitric acid, is deficient in 
available phosphates. 

The use of dilute organic acids renders it possible 
to detect small amounts of readily soluble phosphoric 
acid and potash. It has been stated that when a soil 
has been manured a few years with a phosphate fer- 
tilizer and brought into good condition as to available 
phosphoric acid, a chemical analysis will fail to detect 
any difference in the soil before and after the treat- 
ment with fertilizer. In the case of hydrochloric acid 
as a solvent, this is true, as an acre of soil to the depth 
of one foot weighs about 3,500,000 pounds and 500 
pounds of a phosphate fertilizer would increase the 
total amount of phosphoric acid about 0.0002 per cent, 
which is less than can be accurately determined by 
analysis. When, however, a dilute organic acid is used, 
only the more easily soluble phosphoric acid is dissolved, 
and this readily allows fertilized and unfertilized soils to 
be distinguished. By the use of dilute organic and min- 
eral acids decided differences have been shown between 
fertilized and unfertilized soils. 

101. Sampling Soils. — A composite sample of the 
soil of a field is obtained by taking several small samples 
to a depth of 6 to 12 inches, from different places, and 



THE CHEMICAL COMPOSITION OF SOILS 



87 



uniting them to form one sample. Samples of subsoil 
also are taken from the same places. There is usually 
a sharp line of demarca- 
tion between the surface 
soil and subsoil. It is the 
aim to secure in each case 
as representative a sample 
as possible. All coarse 
stones and roots are re- 
moved and a record is made 
of the amount of these. 
The soil is air-dried, the 
hard lumps are crushed, 
and the material mixed and 
passed through a sieve with 
holes 0,5 mm. in diameter. 
Only the fine earth is used 
for the chemical analysis. 

102. Analysis of Acid- 
soluble Extract of Soils. — 
Ten grams of soil are 
weighed into a soil diges- 
tion flask, and 10 cc. hydro- 
chloric acid (sp. gr. I. II 5) 
are added for every gram of soil used. The soil digestion 
flask is then placed in a hot-water bath and the digestion 
carried on for twelve to thirty-six hours at the temperature 
of boiling water.^^ After digestion is completed the 




Fig. 25. 



Soil Flask and 
tion of Soils. 



S8 SOILS AND FERTILIZERS 

contents of the flask are transferred to a filter and sepa- 
rated into the insohible part, and the acid solution which 
contains the soluble compounds of the various elements. 
The table on page 89 gives a general idea of the 
process of soil analysis. One half of the acid solution 
is used for obtaining the metals as noted on page 89. 
The second half is divided into two portions, — the 
first portion to be used for the determination of phos- 
phoric acid, which is precipitated with ammonium 
molybdate, and the second portion to be used for the 
determination of sulphuric acid, which is precipitated 
as barium sulphate. The carbon dioxide is determined 
in a fresh portion of the original soil, the acid being 
liberated with hydrochloric acid and the carbon dioxide 
retained by absorbents and weighed. The nitrogen 
and humus are determined in separate portions of the 
original soil. The analysis of soils involves the use of 
accurate and well-known methods of analytical chem- 
istry, a discussion of which would not be germane to 
this work. 

103. Value of Soil Analysis. — Opinions differ as to 
the value of soil analysis. It is claimed by some that 
a chemical analysis of a soil is of no practical value 
because it fails to give the amount of available plant 
food. A soil may have, for example, 0.4 per cent of 
potash soluble in hydrochloric acid and still not con- 
tain sufficient available potash to produce a good crop, 
while another soil may contain 0.2 per cent of potash 



THE CHEMICAL COMPOSITION OF SOILS 



89 



^ ^ 



-a c 

C- en 

TO ^ 

o oj 

=-• il 
o ;li 

&-= 
<u 

-I 

o 



■i-S 

s 

biO"rt 

^3 



OS 13 



p o 

il 






(U -O ^ 



-a 
c 






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OJ OJ 



V 



O «3 S 

=" O rt « 

5 a. S "^ 



<u p ii 



c^ .^ 



O rt ^ J 

C Oh 

•Di3 S ca 



X 



J2 O • - 03 <u « 

03 a. *^ .^ i-i-xi ti 
-t^ 03 ' 2 

v; o3 rt 03 .S T! CXd 



o o ^ > 

'■§ a § "So 

"^ ta _Q tj 

^ -k^ OJ 

o ° o 2 s 

o c/2 cxc: 03 



1 d 1^ <u ^ 

•- " OJ 03 =2 

'm -a ^ 3 13 a, 
Pi 



90 SOILS AND FERTILIZERS 

soluble in hydrochloric acid and produce good crops. 
While these conditions are frequently observed, it does 
not necessarily follow that the chemical analysis of a 
soil is of no value, as often the results are not correctly 
interpreted. Then, too, other solvents than hydro- 
chloric acid are used for determining the more active 
forms of plant food. Hydrochloric acid is generally 
used because it represents the limit of the solvent power 
of plants.^ The figures obtained by the hydrochloric 
acid solvent are valuable, as they indicate whenever an 
element is present in amounts too limited for crop pro- 
duction. Suppose a soil contain 0.02 per cent of acid- 
soluble potash ; this would be too small an amount to 
produce good crops. On the other hand, the soil might 
contain 0.5 per cent and yet not have sufficient avail- 
able potash for crop growth. Hence it is that in 
interpreting results, the hydrochloric acid solvent may 
show when a soil is wholly [deficient in any one ele- 
ment, as sometimes occurs, but it does not necessarily 
show a deficiency in the case of a soil rich in acid- 
soluble potash ; this can, however, be approximately 
indicated, by the use of other solvents, as explained 
in previous sections. Hydrochloric acid is mainly val- 
uable in determining the general character of the soil, 
rather than its amount of available plant food. 

104. Interpretation of Soil Analysis. — In the analysis 
of soils their reaction as acid, alkaline, or neutral, should 
be determined, because plant food exists in a different 



THE CHEMICAL COMPOSITION OF SOILS 9I 

form in each class of soils. If a soil contain from 0.3 
to 0.5 per cent or more of lime and from o.i to 0.4 per 
cent of combined carbon dioxide, and is not strongly- 
alkaline, there is a reasonable content of lime car- 
bonate. If, however, the soil contain only a trace of 
carbon dioxide, the lime is not present as carbonate, but 
probably as a silicate, in which case the soil may be 
deficient in active lime compounds. 

In the case of phosphoric acid, a soil which gives an 
alkaline or neutral reaction, contains 0.15 per cent of 
phosphorus pentoxide and is well supplied with organic 
matter and lime, is amply provided with phosphoric acid, 
and under such conditions the use of phosphate ferti- 
lizers is not required, except possibly for special crops. 
Hilgard states that should the per cent of phosphoric 
acid be as low as 0.05, there is, in all probability, a 
deficiency of this element. It frequently happens that 
in acid soils the phosphoric acid is unavailable until a 
lime fertilizer is used to neutralize the acid. 

Soils containing less than 0.07 per cent of total 
nitrogen are usually deficient, and one containing as 
high as 0.15 or 0.2 per cent may fail to respond to 
crop production, but such a case is generally due to 
some abnormal condition of the soil, as lack of alkahne 
compounds which are necessary for nitrification. The 
appearance of the crop is one of the best indications as 
to deficiency of nitrogen. 

A soil which contains less than o.io per cent of 
potash soluble in hydrochloric acid is quite apt to be 



92 SOILS AND FERTILIZERS 

deficient in this element. Soils which contain 0.5 per 
cent or more of lime carbonate will produce good crops 
on a smaller working supply of potash than soils which 
are deficient in lime. As a rule the best agricultural 
soils contain from 0.3 to 0.6 per cent of potash, Sandy- 
soils of good depth may contain less plant food than the 
figures given, and not be in need of fertilizers. 

The best results are obtained from soil analysis when 
an extended study is made of the soils of a locality. 
Then a soil of that region which fails to produce good 
crops can be compared with a productive soil of known 
composition. An isolated soil analysis, like an isolated 
analysis of well water, frequently fails in its object 
because of a lack of proper normal standards for com- 
parison. Where extended series of soil analyses have 
been made, much valuable information has been obtained. 

The term * volatile matter ' of a soil is sometimes incor- 
rectly used for organic matter. The volatile matter in- 
cludes the organic matter and also the water which is held 
in chemical combination, as in the hydrated silicates. 
A soil may have a high per cent of volatile matter and 
contain very little organic matter. Indeed, all clays 
contain from 5 to 9 per cent of water of hydration. 
The per cent of humus, as will be explained in the next 
chapter, does not represent all of the organic matter. 

105. Total and Available Plant Food. — Suppose a 
soil contain 0.40 per cent of acid-soluble potash and 
field experiments indicate there is a deficiency of 



THE CHEMICAL COMPOSITION OF SOILS 93 

available potash. This may be due to some abnormal 
condition of the soil, as an insufficient amount of other 
alkaline compounds, as calcium carbonate, to take the 
place of the potash which has been withdrawn by the 
crop, or lost by leaching, in which case the deficiency of 
available potash can be remedied without purchasing 
soluble potash fertilizer. Where a soil contains only 
0.04 per cent of acid-soluble potash, the purchasing of 
potash fertilizers is more necessary, but with 0.40 per 
cent the way is open to render this available for crops. 
The various ways of rendering acid-insoluble potash and 
other compounds available for crop production, as by 
rotation of crops, use of farm manures, use of lime and 
green manures, or by different methods of cultivation 
have not been sufficiently studied as yet to offer a solu- 
tion to all of the problems of rendering inert plant food 
available. 

106. Distribution of Plant Food. — In studying the 
chemical composition of a soil, the surface soil and sub- 
soil both require consideration. It frequently happens 
that these have entirely different chemical, as well as 
physical, properties, and that a soil fault, as lack of 
potash in the surface soil, is corrected by a high per 
cent of that element in the subsoil. This is particularly 
true of some of the prairie soils, where the surface soils 
generally contain less potash and lime, but more nitrogen 
and phosphoric acid, than the subsoils. When jointly 
considered the surface and subsoil have a good supply 



94 SOILS AND FERTILIZERS 

of available plant food, but if considered separately each 
would have weak points. 

Since plant food is obtained mainly from the silt and 
clay, the amount present in these grades of particles 
determines largely the reserve fertility of a soil. A 
soil in which 70 per cent of the total potash is present 
in the silt and clay is in better condition for crop pro- 
duction than a similar soil with a like amount of potash 
which is present mainly in the sand. Because a soil 
has a given composition, it does not follow that all of 
the different grades of particles have the same composi- 
tion. In fact, the different grades of soil particles in 
one soil may have as varied a composition as is met 
with among different soils-^*^ 

The figures under i in the table give the composition 
of the particles, while under 2 are the results calculated 
on the basis of the total amount of each element in the 
soil. For example, the clay contains 1.47 per cent of 
potash, while 50.8 per cent of the total potash of the 
soil is in the clay particles. 

A soil may contain a low per cent of an element, 
mainly in the finer particles and evenly distributed so 
the crop is better supplied with food than if more were 
present in the larger particles, unevenly distributed. 
The distribution of plant food in the soil has not been 
so extensively studied as the question of total plant 
food. The distribution of plant food in both surface 
soil and subsoil, as well as in the various grades of 
soil particles, is an important factor of fertility. 



THE CHEMICAL COMPOSITION OF SOILS 



95 











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g6 SOILS AND FERTILIZERS 

107. Composition of Typical Soils. — A few examples 
are given, in tabular form, of the chemical composition 
of soils from different regions in the United States, On 
account of variations in the same locality, the figures 
represent the composition of only limited soil areas. 
There have been made in the United States a large 
number of soil analyses which as yet have not been 
compiled or studied in a systematic way. 

108. Alkaline Soils. — When a soil contains enough 
alkaline salts, as sodium sulphate, sodium or potassium 
carbonate or chloride, to be destructive to vegetation, 
it is called an 'alkali' soil. These soils are found in 
semi-arid regions, and wherever conditions have been 
such that the alkaline compounds have not been drained 
from the soil. Occasionally calcium chloride is the 
destructive material. Sodium sulphate is a milder form. 
Alkaline carbonates are destructive to vegetation when 
present to the extent of more than i part per looo parts 
of soil. When evaporation takes place, the alkaline 
compounds are deposited as a coating on the surface 
of the soil. Of these sodium carbonate is one of the 
most injurious; it exerts a solvent action upon the 
humus, forming a black solution which evaporates and 
leaves the so-called 'black alkali.' Many soils sup- 
posed to be strongly alkaHne, because a white coating 
is formed on the surface, simply contain so much lime 
carbonate that a deposit is formed. Excellent soils have 
been passed over as ' alkali ' soils when in reality they 
are limestone soils. 



THE CHEMICAL COMPOSITION OF SOILS 



97 



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SOILS AND FERTILIZERS 





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THE CHEMICAL COMPOSITION OF SOILS 99 

109. Improving Alkali Soils.^^ — When a large tract of 
alkali is to be brought under cultivation, the amount and 
kind of prevailing alkaline compound should be deter- 
mined by chemical analysis. It frequently happens that 
improved drainage, coupled with a judicious irrigation 
system, is all the treatment necessary. If the prevail- 
ing alkali is sodium carbonate, a dressing of land plaster 
may be appHed so as to change the alkali from sodium 
carbonate to sodium sulphate, a less destructive form, 
the reaction being 

Na2C03 + CaS04 = CaCOg + NaaSO^. 

Some shrubs, as greasewood, and weeds, as Russian 
thistle, take from the soil large amounts of alkahne 
matter, and it is sometimes advisable to remove a num- 
ber of such crops so as to reduce the alkali. A shghtly 
beneficial effect is occasionally noticed on small * alkali ' 
spots where straw has been burned and the ashes used, 
forming potassium silicate. As a rule, however, ashes 
are more injurious than beneficial on an 'alkali' soil. 
Irrigation and thorough drainage, if continued long 
enough, will effect a permanent cure. Irrigation with- 
out drainage causes a worse alkaline condition by bring- 
ing to the surface subsoil alkali. All irrigated lands 
should be provided with suitable drainage systems to 
prevent accumulation of alkaline salts. The waters 
from some streams and wells are unsuited for irrigation 
because they contain too much alkaline matter. 

Mildly alkaline soils will usually repay in crop pro- 



lOO SOILS AND FERTILIZERS 

duction all the labor which is expended upon them, and 
when brought under cultivation are frequently very 
fertile. Some alkaline material in a soil is beneficial; 
in fact, many soils would be more productive if they 
contained a small amount. It is the excess of alkali 
that is destructive to plant life. 

When the places are small and located so they can 
be underdrained at comparatively little expense, this 
should be done, as it will prove the best and most per- 
manent way of removing the alkali. Good surface 
drainage should also be provided. Quite frequently a 
quarter or more of the total alkali in the soil will, in a 
dry time, be found near and on the surface. In such 
cases, and if the spots are small, a large amount of the 
alkali can be removed by scraping the surface and then 
carting the scrapings away and dumping them where 
they can do no damage. 

When preparing a mildly alkaline spot for a crop, 
deep plowing should be practiced, so as to open up 
the soil and remove the excess of alkali from the sur- 
face. Where manure, particularly horse manure, can be 
obtained, these spots should be manured very heavily. 
The horse manure, when it decomposes, furnishes acid 
products, which combine with the alkaline salts. The 
manure also prevents rapid surface evaporation. Oats 
are about the safest grain crop to seed on an alkali spot 
because the oat plant is capable of thriving in an alka- 
line soil where many other grain crops fail. 

Alkali soils are usually deficient in available nitro- 



THE CHEMICAL COMPOSITION OF SOILS Id 

gen. The organism which carries on the work of 
changing the humus nitrogen to available forms cannot 
thrive in a strohg alkaline solution. In many of these 
soils, as demonstrated in the laboratory, nitrification 
cannot take place. After thorough drainage and prepa- 
ration for a crop, a few loads of good soil from a fertile 
field sprinkled on alkali spots will do much to encourage 
nitrification, by introducing the nitrifying organisms. 

For a more extended account of the cause of alkali 
soils, and methods for improving them, the student is 
referred to Hilgard's " Soils." 

110. Acid Soils. — When a soil is deficient in active 
alkali, and there is an excess of organic material, humic 
acid is formed from the decay of the animal and vege- 
table matter. Acid soils are readily detected by the 
reaction which they give with sensitive litmus paper. 
In making the test the moistened soil is pressed against 
blue litmus paper, which changes to red in the presence 
of free acids. Acid soils are made productive by using 
lime and other alkaline material to neutralize the humic 
acid before applying farm and other manures. Acid soils 
are not suitable for the production of clover and legumes. 

Experiments by Wheeler at the Rhode Island Ex- 
periment Station indicate that there are large areas 
of acid soils in the eastern states which are much 
improved when treated with air-slaked lime.^^ There 
is great difference in the power of plants to live in 
acid soils. Some agricultural crops as legumes are par- 



I02 SOILS AND FERTILIZERS 

ticularly sensitive, while many weeds have such strong 
power of endurance that they thrive in the presence of 
acids. Weeds frequently reflect the character of a soil 
as to acidity, in the same way that an alkali soil is 
indicated by the plants produced. The acid and alka- 
line compounds of the soil greatly influence the bacterial 
flora. In the presence of strong acids or alkalis, many 
of the bacterial changes necessary for the elaboration of 
plant food fail to take place. 

THE ORGANIC COMPOUNDS OF SOILS 

111. Sources of the Organic Compounds of Soils. — 
The organic compounds of soils are composed of the 
elements carbon, hydrogen, oxygen, and nitrogen. 
When vegetable and animal material undergoes decay 
in contact with the soil, compounds, as carbon dioxide, 
water, ammonia,^^ organic acids, and various derivatives 
are formed, while some of the organic acids unite with 
the. minerals of the soil to form humates. Micro- 
organisms take an important part in the decay of ani- 
mal and vegetable matter and the production of organic 
compounds. In some soils, the organic compounds of 
plants, as cellulose, proteids, and carbohydrates, are 
present, while in others they have undergone partial 
oxidation. Some authorities claim that a portion of the 
initial organic matter of soils is the result of the work- 
ings of carbon assimilating micro-organisms. The main 
source of the soil's organic compounds, however, is the 



THE CHEMICAL COMPOSITION OF SOILS IO3 

accumulated animal and vegetable remains in various 
stages of decay. The organic matter of soils is a 
mechanical mixture of a large number of organic com- 
pounds, many of which have not yet been studied. 

112. Classification of the Organic Compounds. — Vari- 
ous attempts have been made to classify the organic 
compounds of the soil. An old classification by 
Mulder ^^ was humic, ulmic, crenic, and approcrenic 
acids. None of these contain more than 4 per cent 
nitrogen, while organic matter with 8 to 10 per cent 
and in some cases 18 per cent is quite frequently 
met with ; hence this classification is incomplete as it 
includes only a part of the organic compounds of the 
soil. For practical purposes the organic compounds of 
soils may be divided into three classes: (i) those of low 
nitrogen content, i to 4 per cent of nitrogen ; (2) those 
of medium nitrogen content, 5 to 10 per cent; and (3) 
those of high nitrogen content, 11 to 20 per cent. 

113. Humus. — The term ' humus ' is employed to 
designate the most active of the organic compounds ; 
it is the animal and vegetable matter of the soil in 
intermediate forms of decomposition. From different 
soils, it is extremely varied in composition ; in one soil 
it may have been derived mainly from cellulose, while 
in another from a mixture of cellulose, proteid bodies, 
and other organic compounds. The term 'humus,' unless 
quaHfied, is a very indefinite one. Humus is obtained 



I04 SOILS AND FERTILIZERS 

by extracting the soil with a dilute alkali, as ammonium 
hydroxide, after treating with a dilute acid to remove 
the lime which renders the humus insoluble. 

114. Humification and Humates. — When the animal 
and vegetable matter incorporated with soils undergoes 
decomposition, there is a union of some of the organic 
compounds with the base-forming elements. The decay- 
ing organic matter produces organic products of an acid 
nature. The organic acids and the base-forming 
products unite to form humates or organic salts, which 
are neutral bodies. This process is humification.^^ 

Humic acid + calcium carbonate = calcium humate + COg. 
Humic acid + potassium chloride = potassium humate and solu- 
ble chlorides. 

That a union occurs between the organic matter and 
the soil has been demonstrated by mixing with soils 
known amounts of definite organic compounds and 
various organic materials, as cow manure, green clover, 
meat scraps, and sawdust, and allowing humification to 
go on for a year or more. After humification had 
taken place, the humus extracted from the soil con- 
tained more potash and phosphoric acid, than were 
present in the humus of the original soil and the humus- 
forming material, showing a chemical change had taken 
place between the organic matter and the soil. The 
power of various organic substances to produce humates 
is illustrated in the following table : ^^' ^^ 



THE CHEMICAL COMPOSITION OF SOILS 



105 



C01V mafui?-e Jnnnits : 

In original manure and soil 

In final humus product (after humifica- 
tion) 

Gain in humic forms 

Green cloiier humus : 

in original soil and clover ..... 

In final humus product 

Gain in humic forms 

Afeal scrap humus : 

In original meat scraps and soil . . 

In final humus product 

Gain .■ . . 

Sawdust hu/iius : 

In original sawdust and soil .... 

In final humus product . . . . 
Oat straw humus : 

In original straw and soil 

In final humus product 

Wheat gliadiit humus : 

In original gliadin and soil 

In final humus product 

Gain 

Egg albjitnin humus : 

In original albumin and soil .... 

In final humus product 

Gain 



Humic Phos- 
phoric Acid 


Humic 
Potash 


Grams 


Grams 


1. 17 


1.06 


1.62 


1.27 


0.45 


0.21 


3.21 


5.26 


374 


4-93 


0-53 


0-33 

(Loss) 


1.07 


0.25 


1. 18 


0.36 


O.II 


O.II 


0.85 


0.67 


0.78 


0.70 


1.02 


2.42 


1.03 


2.41 


1.055 


0.19 


1.220 


0.24 


0.165 


0.05 


I.OI 


0.20 


I. II 


0.24 



0.04 



io6 



SOILS AND FERTILIZERS 



115. Comparative Value and Composition of Humates. 
— The humus produced from a nitrogenous material, 
as meat scraps, is more valuable than from cellulose 
bodies, as sawdust, because the former has greater 
power of combining with the phosphoric acid and 
potash of the soil. The non-nitrogenous compounds, 
as cellulose, starch, and sugar, undergo fermentation but 
seem to possess little, if any, power to form humates. 
There is also a great difference in soils as to their 
humus-producing power. Soils deficient in lime or al- 
kaline compounds possess only a feeble power to pro- 
duce humates. There is too a marked variation in 
the composition of the humus from different kinds of 
organic matter. Straw, sawdust, and sugar, materials 
rich in cellulose and other carbohydrates, yield a humus 
characteristically rich in carbon and poor in nitrogen. 
Materials rich in nitrogen, like meat scraps, green clover, 
and manure, produce a more valuable humus, rich in 
nitrogen and possessing the power to combine with the 
potash and phosphoric acid of the soil to form humates. 

Composition of Humus produced by 





Cow 

manure 


Green 

clover 


Meat 

scraps 


Wheat 
flour 


Oat 

straw 


Saw- 
dust 


Sugar 


Carbon 
Hydrogen 
Nitrogen 
Oxygen 


41.95 
6.26 
6.16 

45-63 


54.22 

3-40 
8.24 

34-14 


48-77 

4-30 

10.96 

35-97 


51.02 
3.82 
5.02 

40.14 


54-3° 
2.48 
2.50 

40.72 


49.28 

3-33 

0.32 

47-07 


57-84 
3-04 
0.08 

39-04 


Total 


100.00 


100.00 


100.00 


100.00 


100.00 


100.00 


100.00 



THE CHEMICAL COMPOSITION OF SOILS 



107 



Carbon . 
Hydrogen 
Nitrogen 
Oxygen . 



Highest 



57.84 

6.26 

10.96 

47.07 



Lowest 



41.95 

2.48 
0.08 

34-14 



Difference 



15.89 

10.88 
12.93 



Variations in composition are noticeable. The hu- 
mus produced from each material, as green clover, oat 
straw, or sawdust, is different from that produced from 
any other material. The humus from green clover is 
very complex in nature. It contains both nitrogenous 
and non-nitrogenous compounds, and each class has a 
different action in humification processes; hence it fol- 
lows that the green clover humus must be a complex 
mixture of both nitrogenous and non-nitrogenous bodies. 

The nature of the humus, whether nitrogenous or 
non-nitrogenous, is important. Humus produced from 
sawdust and humus from meat scraps may be taken as 
types of non-nitrogenous and nitrogenous humus. 



116. Value of Humates as Plant Food. — Various 
opinions have been held regarding the actual value, as 
plant food, of this product from partially decayed an- 
imal and vegetable matter. Humus was formerly re- 
garded as composed only of carbon, hydrogen, and 
oxygen, and inasmuch as plants obtain these elements 
from water and from the carbon dioxide of the air, no 
value was assigned to it. Later investigators added 



io8 



SOILS AND FERTILIZERS 




volafilemamr 



nitrogen to the list, but stated that the nitrogen, when 
combined with the humus and before undergoing fer- 
mentation, was of no value as plant food. 

Recent investigations have proved that the mineral 
elements combined with the organic matter of soils are 
of value as plant food,^ and that crops grown on the 

black soils of Russia 
obtain a large part of 
their mineral food 
from organic combi- 
nations.^'* Culture ex- 
periments show that 
plants like oats and 
rye may obtain their 
mineral food entirely 
from humate sources. 
Seeds when planted 
in a mixture of pure 
sand and neutral 
humates from fertile 
soils, produced per- 
fect plants. In order 
to secure normal con- 
ditions, a little Hme 
was added to prevent the formation of humic acid, and 
the organisms found in fertile fields were introduced. 
The following results are given of oats which were 
grown when the only supply of mineral food was in 
humate forms : 



Ibtal /n30/ui?/e/iatfer 



Fig. 26. Graphic Composition of 200 Soils, 
showing the Proportional Amounts of the 
Various Soil Constituents. 



Nitrogen. 2. Potash. 3. Phosphoric 



acid. 



THE CHEMICAL COMPOSITION OF SOILS 



109 



Nitrogen and Ash Elements^ 



Nitrogen .... 

Potash 

Soda 

Lime 

Magnesia .... 
Iron ..... 
Phosphoric anhydride 
Sulphuric anhydride 
Silicon 



In Six Oat 


In Six Mature 


Seeds 


Plants 


Gram 


Gram 


0.0040 


0.0556 


00013 


0.0640 


O.OOOI 


0.0079 


0.0002 


0.0249 


0.0005 


o.oi 10 




0.0064 


0.0016 


0.0960 


O.OOOI 


0.0090 


0.0026 


0.7300 



The facts that plants feed on humate compounds, and 
decaying animal and vegetable matter produce humates 
from the inert potash and phosphoric acid of the soil, 
have an important bearing upon crop production in 
pointing out a way by which inert plant food may be con- 
verted into more active and available forms. This 
also explains that stable manure is valuable partly 
because it makes the inert plant food of the soil more 
available. 



117. Mineral Matter combined with Humus. — When 
the humus compounds are separated from a soil, they 
contain appreciable amounts of phosphorus, potassium, 
and compounds of other elements which are soluble in 
the reagents used for obtaining the humus. If the 



no 



SOILS AND FERTILIZERS 



humus materials are precipitated and purified by wash- 
ing, the impurities are largely removed and the mineral 
elements which are chemically united with and form a 
part of the humus can then be determined. Analyses 
of eight samples of purified humus ash, from produc- 
tive prairie soils, gave the following average : ^ 





Per Cent 


Ash (precipitated humus) 


12.24 


Composition of ash : 




Silica 


61.97 


Potash, KoO . 














7.20 


Soda, NagO 














8.13 


Lime, CaO 














0.09 


Magnesia, MgO 














0.36 


Ferric oxide, Fe.^Oo . 














3.12 


Alumina, AUO^ 














348 


Phosphoric acid, PjO^ 














12.37 


Sulphuric acid, SO3 














0.98 


Carbonic acid, CO, 














1.64 



118. Amount of Plant Food in Humate Forms. — In a 

prairie soil containing 3.5 per cent of humus there are 
present 100,000 pounds of humus per acre. Combined 
with this humus are from 500 to 1500 pounds each of 
phosphoric acid and potash. Similar soils which have 
been under long cultivation without the restoration of 
any humus, contain from 300 to 500 pounds each of 
humic potash and phosphoric acid.^ A decline in crop- 
producing power has in many cases been brought 



THE CHEMICAL COMPOSITION OF SOILS I 1 1 

about by the loss of the plant food combined with the 
humus. 

119. Loss of Humus. — Loss of humus from soils is 
caused by oxidation and by fires. Any method of 
cultivation which accelerates oxidation reduces the 
humus content. In many of the western prairie soils 
which have been under continuous grain cultivation 
for thirty years or more, the amount of humus has been 
reduced one half. Summer fallowing also causes a loss 
of humus. When land is continually under the plow, 
and no manures are used, the humus is rapidly oxidized, 
and there is left in the soil only the organic matter that 
is slow to decay. 

Forest and prairie fires have been very destructive 
to the organic compounds of the soil. A soil from 
Hinckley, Minn., before the great forest fire of 1893, 
showed 1.69 per cent humus and 0.12 per cent nitro- 
gen. ^^ After the fire there were present 0.41 per cent 
humus and 0.03 per cent nitrogen. The forest fire 
caused a loss of 2500 pounds of nitrogen per acre. In 
clearing new land, particularly forest land, there is 
frequently an unnecessary destruction of humus mate- 
rials. Instead of burning all of the vegetable matter, it 
would be better economy to leave some in piles for 
future use as manure. When all of the vegetable mat- 
ter has been burned, two or three good crops are 
obtained, but the permanent crop-producing power of 
the land is reduced because of the loss of nitrogen and 



112 



SOILS AND FERTILIZERS 



humus. When the vegetable matter has been only 
partially removed, the crops at first may be smaller, 
but in a few years returns will be greater than if all 
of the vegetable matter had been burned. 

120. Physical Properties of Soils influenced by Humus. 

— The physical properties of a soil may be entirely 
changed by the addition or the loss of humus. The 
influence of humus upon the weight, color, heat, and 
water-retaining power of soils is discussed in the chap- 
ter on the physical properties of soils. Soils reduced in 
humus content have less power of storing up water and 
resisting drought. This fact is illustrated in the follow- 
ing table : ^^ 

Per Cent Water 



In Soil 



After io Hours' 
Exposure in 
Tray, to Sun 



Soil rich in humus (3.75 per cent) . . . 
Adjoining soil poorer in humus (2.50 per cent) 



16.48 
12.14 



6.12 
3-94 



121. Humic Acid. — In the absence of calcium car- 
bonate or other alkaline material, the vegetable matter 
of soils through processes of decay may form organic 
acids destructive to the growth of some crops. The com- 
position and physical properties of these organic acids 
have never been determined, and the indefinite term 
' humic acid ' has been applied to them. Succinic acid 



THE CHEMICAL COMPOSITION OF SOILS 



113 



has been reported present in peaty soils. Acid soils 
can be distinguished by their action upon blue litmus 
paper, and the acidity can be readily corrected by the use 
of lime or wood ashes. A soil may, however, give an 
acid reaction and contain a fair amount of lime as a 
silicate. Studies conducted by the Rhode Island Ex- 
periment Station indicate that the areas of acid soils are 
quite extensive. 




Fig. 27. Humus from Old Soil. 



122. Soils in Need of Humus. — Sandy and sandy 
loam soils that have 
been cultivated for a 
number of years to 
corn, potatoes, and 
small grains without 
rotation of crops or the 
use of stable manures 
are deficient in humus. Clay soils, as a rule, are not in 
need of humus so much as loam and sandy soils. The 

mechanical condition of 
heavy clay is, however, im- 
proved by the addition of 
humus-forming material. 
The addition of humus to 
loam and sandy soils is 
beneficial in preventing 
drifting, because it binds together the soil particles. 
There are but few arable soils, under ordinary cultiva- 
tion, to which it is not safe to add humus-forming mate- 



'==^-^^xy^e/7^^ 



' ■ .f'Cart'on- 



jiL 






Fig. 28. Humus from New Soil. 



114 



SOILS AND FERTILIZERS 



rials either alone or jointly with lime. Ordinary prairie 
soils, for the first ten years after breaking, are usually 
well supplied. Swampy, peaty, and muck soils contain 
large amounts ; in fact, they are often overstocked and 
are improved by reducing the humus content. 'Alkali' 
soils are usually deficient in humus. 

123. Active and Inactive Humus. — When soil has 
been long under cultivation, and no manures have been 
used, the nitrogen and mineral matters combined with 
the humus are reduced. The humus from long-culti- 
vated fields contains a higher per cent of carbon than 
from well-manured or new land; it is also less active 
because of the carbon which does not readily undergo 
oxidation.^ 



humos from 
New Soil 



Per cent 



Humus from 
Old Soil 



Per cent 



Carbon 

Hydrogen 

Oxygen 

Nitrogen 

Ash 

Total humus material 



44.12 
6.00 

35-16 
8.12 
6.60 



5-3° 



50.10 

4.80 

3370 
6.50 
4.90 



3-38 



124. Influence of Different Methods of Farming upon 
Humus. — The system of farming has a direct effect 
upon the humus content and the composition of the 



THE CHEMICAL COMPOSITION OF SOILS 



115 



soil. Where the crops are systematically rotated, live 
stock is kept, and the manure judiciously used, the 
crop-producing power of the land is not lowered, as in 
the case of the one-crop system. The influence of dif- 
ferent systems of farming upon the humus content and 
other properties of the soil may be observed in the fol- 
lowing table : ^^ 



Character of Soil 


3 


u 
0. 

M c 






Phosphoric acid 
combined with 
humus 
Per cent 


Ml 

C 

'•3 


1. Cultivated thirty-five years; 

rotation of crops and ma- 
nure ; high state of pro- 
ductiveness 

2. Originally same as i ; con- 

tinuous grain cropping for 
thirty-five years ; low state 
of productiveness . . . 

3. Cultivated forty-two years ; 

systematic rotation and 
manure ; good state of pro- 
ductiveness 

4. Originally same as 3 ; culti- 

vated thirty-five years ; no 
systematic rotation or ma- 
nure ; medium state of pro- 
ductiveness 


70 
72 
70 

67 


3-32 
1.80 
346 

2.45 


0.30 
0.16 
0.26 

0.21 


0.04 
0.0 1 
0.03 

0.03 


48 
39 
59 

57 



CHAPTER IV 

NITROGEN OF THE SOIL AND AIR, NITRIFICATION, 
AND NITROGENOUS MANURES 

125. Importance of Nitrogen as Plant Food. — The 
illustration (Fig. 29) shows an oat plant which received 
no nitrogen, while compounds containing potassium, 
phosphorus, calcium, and other essential elements of 
plant food were liberally supplied. Observe the pecul- 
iar and restricted growth and the limited root develop- 
ment. The leaves were yellowish, showing lack of 
nitrogen for chlorophyll formation. 

In the absence of nitrogen a plant makes no ap- 
preciable growth. With only a limited supply, growth 
is begun in a normal way ; but as soon as the available 
nitrogen is used up, the lower and smaller leaves begin 
gradually to die down from the tips, and all of the 
plant's energy is centered in one or two leaves. In one 
experiment when only a small amount of nitrogen was 
supplied, the plant struggled along in this way for 
about nine weeks, making a total growth of but six 
and one half inches.^ Just at the critical point when 
the plant was dying of nitrogen starvation, a few mil- 
ligrams of calcium nitrate were given. In thirty-six 
hours the plant showed signs of renewed life, the leaves 

116 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 11/ 



assumed a deeper green, new growth was begun, and 
finally four seeds were produced. 
During the time of seed formation 
more nitrogen was added, but with no 
beneficial result. All of the essential 
elements for plant growth were liber- 
ally provided, except nitrogen, which 
was very sparingly supplied, until near 
the period of seed formation. 

When plants have reached a certain 
period in their development, and have 
been starved for want of nitrogen, the 
later application of this element does 
not produce normal growth, as the en- 
ergy of the plant appears to have been 
used up in searching for food. Nitro- 
gen, as well as potash, lime, and phos- 
phoric acid, are all necessary while 
plants are in the first stages of growth. 

In the case of wheat, nitrogen is as- 
similated more rapidly than are any 
of the mineral elements. Before the 
plant heads out, over 85 per cent of 
the total nitrogen required has been 
taken from thesoil.^*^ Corn also absorbs 
all of its nitrogen from four to five 
weeks before the crop matures. Flax 
takes up 75 per cent during the first fifty days of 
growth. ^^ 




Fig. 29. Oat Plant 
grown without Ni- 
trogen. 



Il8 SOILS AND FERTILIZERS 

Nitrogen is demanded by all crops ; it forms the chief 
building material for the proteids of plants. In the ab- 
sence of sufficient nitrogen, the rich green color is not 
developed ; the foliage is of a yellowish tinge. Nitro- 
gen is one of the constituents of chlorophyll, the green 
coloring matter of plants ; hence when there is a lack of 
nitrogen only a limited amount of chlorophyll can be 
produced. Plants with large, well-developed leaves of 
a rich green color are not suffering for this element. 
Nitrogenous fertilizers have a tendency to produce a 
luxurious growth of foliage, deep green in color. 



ATMOSPHERIC NITROGEN AS A SOURCE OF PLANT 

FOOD 

126. Early Views. — In addition to carbon, hydrogen, 
and oxygen, which form the organic compounds of 
plants, it was known as early as the beginning of the 
present century that plants also contain nitrogen. The 
sources of carbon, hydrogen, and oxygen for crop pur- 
poses were much easier to determine and understand 
than the sources of nitrogen. Priestley, the discoverer 
of oxygen, believed that the free nitrogen of the air 
was a factor in supplying plant food. De Saussure ar- 
rived at just the opposite conclusion. Neither of these 
assumptions was convincing because methods of chem- 
ical analysis had not yet been sufficiently perfected to 
solve the question.^ 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES II 9 

127. Boussingault's Experiments. — Boussingault was 
the first to make a careful study of the subject. In a 
prepared soil, free from nitrogen, and containing all of 
the other elements necessary for plant growth,' he grew 
clover, wheat, and peas, carefully determining the 
nitrogen in the seed. The plants were allowed free 
access to the air, being simply protected from dust, and 
were watered with distilled water. But little growth 
was made. At the end of two months the plants were 
submitted to chemical analysis, and the amount of ni- 
trogen present was determined. 

The results are given in the following table :*^ 



Nitrogen 



Clover, 2 mos. 

Clover, 3 mos. 

Wheat, 2 mos. 

Wheat, 3 mos. 

Peas, 2 mos. 



In Seed Sown 
Gram 



O.II 

O.I 14 

0.043 
0.057 
0.047 



In Plant 
Gram 



0.12 

0.156 

0.04 

0.06 

O.IO 



Gain 

Gram 



O.OI 
0.042 
-0.003 
0.003 
0.053 



Boussingault concluded that when plants growing in 
a sterile soil were exposed to the air, there was with 
some a slight gain of nitrogen, but that the amount 
gained from atmospheric sources was not sufficient to 
feed the plant and allow it to reach full maturity. By 
many these results were not accepted as conclusive. 

Fifteen years later (1853) Boussingault repeated his 



I20 



SOILS AND FERTILIZERS 



experiments, but in a different way. The plants were 
now grown in a large carboy with a limited volume of 
air so as to cut off all sources of com- 
bined nitrogen, as traces of ammonia, 
nitrates, and nitrites. By means of 
a second glass vessel {B, Fig. 30) the 
carboy was kept liberally suppHed 
with carbon dioxide, so that plant 
growth would not be checked for 
lack of this material. When experi- 
ments were carried on in this way, 
using a fertile soil, the plants reached 
full maturity ; but when a soil free 
Plants grown from nitrogcn was used, plant growth 
was soon checked. A general sum- 
mary of this work is given in the following table : ^^ 




Fig. 30, 

in Carboy 



Nitrogen 





In Seeds 
Gram 


In Plant 
Gram 


Loss 
Gram 


Dwarf beans .... 

Oats 

White lupines .... 
Garden cress .... 


O.IOOI 
0.0109 
0.2710 
0.0013 


0.0977 
0.0097 
0.2669 
0.0013 


— 0.0024 

— 0.0012 

— 0.0041 



These experiments show that with a sterilized soil, 
and all sources of combined atmospheric nitrogen cut 
off, the free nitrogen of the air takes no part in the food 
supply of the plant. . 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 121 

In 1854 Boussingault again repeated his experiments 
on nitrogen assimilation. This time he grew the plants 
in a glass case so constructed that there was free 
circulation of air from which all combined nitrogen had 
been removed. These experiments were similar to his 
second series, except the plants were not grown in a 
limited volume of air. The results obtained showed 
that the free nitrogen of the air, under the conditions of 
the experiment, took no part in the food supply of the 
plants. If anything, there was less nitrogen recovered in 
the dwarfed plants than there was in the seed sown. 

128. Villa's Results. — About the same time Ville 
carried on a series of experiments of like nature, but in 
a different way, and arrived at just the opposite con- 
clusion. His experiments indicated that plants are 
capable of making liberal use of the free nitrogen of 
the air for food purposes. The directly opposite con- 
clusions of Boussingault and Ville led to a great deal of 
controversy. The French Academy of Science took up 
the question, and appointed a commission to review the 
work of Ville. The commission consisted of six promi- 
nent scientists. They reported that " M. Ville's con- 
clusions are consistent with his labor and results."^^ 

129. Work of Lawes and Gilbert. — A little later 
Lawes and Gilbert carried on such extensive experi- 
ments under a variety of conditions as to remove all 
doubt regarding the plants' source of nitrogen. Plants 



122 SOILS AND FERTILIZERS 

were grown in sterilized soils, in prepared pumice stone, 
and in soils with a limited quantity of nitrogen beyond 
that contained in the seed. Different kinds of plants 
were experimented with. The work was carried on with 
the utmost care and with apparatus so constructed as to 
eliminate all disturbing factors. The results in the 
aggregate clearly show that plants, when acting in a 
sterile medium, are unable to make use of the free 
nitrogen of the air for the production of organic 
matter.^^ 

130. Atwater's Experiments. — Atwater carried on 
similar experiments in this country.*^ His results in- 
dicate that when seeds germinate they lose a small part 
of their nitrogen, and when legumes are grown in a 
sterile soil, but are subsequently exposed to the air, a 
fixation of nitrogen may occur. He ascribed this gain to 
micro-organisms or other agencies. 

131. Field and Laboratory Tests. — By a five years' 
rotation of clover and other leguminous plants, Lawes 
and Gilbert found a soil gained from 200 to 400 
pounds of nitrogen per acre, in addition to that removed 
in the crop, while land which produced wheat contin- 
uously, gradually lost nitrogen. The amount in the 
subsoil remained nearly the same. These facts plainly 
indicated that crops like clover have the power of gain- 
ing nitrogen from unknown sources. The results of 
prominent German agriculturists led to the same con- 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 23 

elusion. It was known that wheat grown after clover 
gave as good results as when nitrogenous manures were 
used, but for many years this was unexplained. 

Laboratory experiments with sterilized soils do not 
represent the normal conditions of growing crops, where 
all of the bacteriological agencies of the soil, the air, 
and the plant are free to act. Experiments show that 
these agencies have an important bearing upon plant 
growth. 

In the work of the different investigators prior to 
1888, plants were grown mainly in sterilized soils, and 
under such conditions they were unable to make use of 
the free nitrogen of the air, except when the soils were 
subsequently inoculated from the air. 

132. Hellriegel's Experiments. — Hellriegel grew le- 
guminous plants in nitrogen-free soils. One set of 
plants was watered with distilled water, while another 
had in addition small amounts of leachings from an old 
loam field. The plants watered with distilled water 
alone made but little growth, while those watered with 
the loam leachings reached full maturity and contained 
something like a hundred times more nitrogen than was 
in the seed sown. The dark green color also was 
developed, showing the presence of a normal amount of 
chlorophyll. The roots of the plants had well-formed 
swellings or nodules, while those that were watered with 
distilled water alone had none. The loam leachings 
contained only a trace of nitrogen.*^ 



124 



SOILS AND FERTILIZERS 



133. Experiments of Wilfarth. — Experiments by 
Wilfarth give more exact data regarding the amount 
of nitrogen taken from the air. Two plots of lupines 
were grown ; one was watered with distilled water, while 
the other received in addition a small amount of leach- 
ings from an old lupine field. 



Watered with Distilled Water 


Watered with Distilled Water 
AND Soil Leachings 


Dry matter 
Grams 


Nitrogen 
Grams 


Dry matter 
Grams 


Nitrogen 
Grams 


0.919 
0.800 
0.921 
1 .02 1 


0.015 
0.014 
0.013 
0.013 


44-72 
45.61 
44.48 
42-45 


1.099 

I-I53 
1. 195 

1-337 



These experiments have been verified by many other 
investigators until the fact has been estabHshed that 
leguminous plants may, through the agency of micro- 
organisms, make use of the free nitrogen of the air. 
When legumes were grown in closed vessels and the air 
was analyzed, it was found that there was a loss of 
nitrogen from the air proportional to that gained by the 
plants. 

The work of Hellriegel was not accidental, but the 
result of careful and systematic investigation. As early 
as 1863 he observed that clover would develop along the 
roadway in sand in which there was scarcely a trace of 
combined nitrogen. 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 25 

134. Composition of Root Nodules. — The root nodules 
referred to are particularly rich in nitrogen. In one 
experiment, the light-colored and active ones contained 
5.55 per cent, while those dark-colored and older con- 
tained 3.21 per cent, and all the nodules of the root, 
both active and inactive, contained 4.60 per cent nitro- 
gen. The root itself contained 2.21 per cent.*^ 

The root nodules also contain definite and character- 
istic micro-organisms, and it was the spores of these or- 
ganisms that were in the soil extract in both Hellriegel's 
and Wilfarth's experiments. In the sterilized soils they 
were not present. These organisms found in root nod- 
ules are the essential agents which aid in the fixation of 
the free nitrogen of the air, and in its ultimate use as 
plant food. The nitrogen assimilated by the micro- 
organisms in the nodules of the legumes is in part ap- 
propriated by the crop, which unaided is incapable of 
making use of the free nitrogen of the air. 

135. Nitrogen in the Root Nodules returned to the 
Soil. — Ward has shown that when clover roots decay, 
the organisms and nitrogen present in the nodules are 
distributed within the soil.^^ Hence, whenever a legu- 
minous crop is raised, nitrogen is added to the soil 
instead of being taken away, as in the case of a grain 
crop. The amount of nitrogen returned to the soil by 
a leguminous crop as clover varies with the growth 
of the crop. In the roots of a clover crop a year old 
there are from 20 to 30 pounds of nitrogen per acre. 



126 SOILS AND FERTILIZERS 

while in the roots and cuhns of a dense clover sod, 
two or three years old, there may be lOO pounds or 
more of nitrogen, not including that which has been 
added to the soil by the accumulative action of the crop. 
Peas, beans, lucern, cow peas, and all legumes possess 
the power of fixing the free nitrogen of the air by means 
of micro-organisms. The micro-organisms associated with 
one species, as clover, differ from those associated with 
another, as lucern. The amount of nitrogen which the 
various legumes return to the soil is variable. 

Hellriegel's results are of the greatest importance to 
agriculture, because they show how the free nitrogen of 
the air can be utilized indirectly as food by crops unable 
to appropriate it for themselves. 

THE NITROGEN COMPOUNDS OF THE SOIL 

136. Origin of the Soil Nitrogen. — The nitrogen of 
the soil is derived chiefly from the accumulated remains 
of animal and vegetable matter. The original source 
of the soil nitrogen, that is, the nitrogen which furnished 
food to support the vegetation from which our present 
stock of soil nitrogen is obtained, was probably the free 
nitrogen of the air. All of the ways in which the free 
nitrogen of the air has been made available to plants of 
higher orders which require combined nitrogen are not 
known. It* is supposed, however, that this has been 
brought about by the workings of lower forms of plant 
life,and by micro-organisms. Whatever these agencies, 
they do not appear to be active in a soil under high cul- 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 12/ 

tivation, because the tendency of ordinary cropping is to 
reduce the supply of soil nitrogen. 

137. Organic Nitrogen of the Soil. — In ordinary soils 
the nitrogen is present mainly in organic forms com- 
bined with the carbon, hydrogen, and oxygen as humus, 
and to a less extent with the mineral elements, forming 
nitrates and nitrites. The organic forms of nitrogen, 
it is generally considered, are incapable of supplying 
plants with nitrogen for food purposes until the process 
known as nitrification has taken place. The nitrogenous 
organic compounds in cultivated soils are derived mainly 
from the undigested protein compounds of manure and 
from the nitrogenous compounds in crop residues, and 
are present mainly as insoluble proteids.^^ When de- 
composition occurs, amides, organic salts, and other 
allied bodies are without doubt produced as interme- 
diate products before nitrification takes place. The or- 
ganic nitrogen of the soil may be present in exceedingly 
inert forms similar to that in leather, as in many peaty 
soils where there are large amounts of inactive organic 
compounds rich in nitrogen. In other soils the nitrogen 
is less complex. The organic nitrogen of the soil may 
vary in complexity from forms, like the nitrogen of urea, 
which readily undergo nitrification, to forms like that in 
peat, which nitrify with difficulty, 

138. Amount of Nitrogen in Soils. — The fertility 
of any soil is dependent, to a great extent, upon the 



128 SOILS AND FERTILIZERS 

amount and form of its nitrogen. In soils of the 
highest fertility there is usually present from 0.2 to 
0.3 per cent of total nitrogen, equivalent to from 
7000 to 10,000 pounds per acre to the depth of one 
foot. Many soils of good crop-producing power contain 
as low as 0.12 per cent. There is usually two or three 
times more nitrogen in the surface soil than in the sub- 
soil In sandy soils which have been allowed to decHne 
in fertility, there may be less than 0.04 per cent. Of 
the total nitrogen in soils there is rarely more than 2 
per cent at any one time in forms available as plant 
food.** A soil with 5000 pounds of total nitrogen per 
acre may contain less than 100 pounds of available nitro- 
gen soluble in the soil water, of which only a part is 
assimilated by the roots of crops. Hence it is that a 
soil may contain a large amount of total nitrogen, and 
yet be deficient in available nitrogen. 

139. Amount o4 Nitrogen removed in Crops. — The 
amount of nitrogen removed in crops ranges from 25 to 
100 pounds per acre, depending upon the nature of the 
crop. It does not necessarily follow that the crop which 
removes the largest amount of nitrogen leaves the land 
in the most impoverished condition. Wheat and other 
grains, while they do not remove so much in the crop, 
leave the soil more exhausted than if other crops were 
grown. This, as will be explained, is caused by the loss i 
of nitrogen from the soil in other ways than through the 
crop. 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 129 



Wheat, 20 bushels . 
Straw, 2000 pounds 

Total . 
Barley, 40 bushels . 
Straw, 3000 pounds 

Total . 
Oats, 50 bushels . . 
Straw. 3000 pounds 

Total . 
Flax, 15 bushels . . 
Straw, 1800 pounds . 

Total . 
Potatoes, 1 50 bushels 
Corn, 65 bushels 
Stalks, 3000 pounds 

Total. 



Pounds of 

Nitrogen per 

Acre removed 

IN Crop^ 



25 
10 

35 
28 
12 

40 

35 

50 
39 
_^ 

54 

40 
40 

ii 

75 



140. Nitrates and Nitrites. — Nitrogen in the form of 
nitrates and nitrites varies from mere traces to 150 
pounds per acre. Soils with large amounts of nitroge- 
nous humus and lime may contain for short periods as 
high as 300 pounds of nitrates and 15 pounds of nitrites, 
calculated as sodium salts. Some soils contain more 
nitrates than are utilized by crops as food, and plants 
may assimilate more than they can convert into protein, 

K 



I30 SOILS AND FERTILIZERS 

Wheat, corn, and other crops grown on rich soils may 
contain both nitrates and nitrites as normal constituents. 
King reports nitrates in the growing crop in much larger 
amounts than in the soil water. As the crop matures 
the nitrate content of the plant declines. Calcium ni- 
trate is the usual form, especially in soils which are 
sufficiently supplied with calcium carbonate to allow 
nitrification to progress rapidly. Nitrates and nitrites 
are the most valuable forms of nitrogen for plant food. 
Both are produced from the organic nitrogen of the soil. 
A nitrate is a compound composed of a base element as 
sodium, potassium, or calcium, combined with nitrogen 
and oxygen. A nitrite contains less oxygen than a nitrate. 
Potassium nitrate, KNO3, sodium nitrate, NaNOg, 
and calcium nitrate, Ca(N03)2 are the nitrates which 
are of most importance in agriculture. The nitrites, as 
potassium nitrite, KNOg, are present to a less extent 
than the nitrates. Nitrates and nitrites are found in 
surface well waters contaminated with animal and vege- 
table matter. Many well waters possess some material 
value as a fertilizer on account of the nitrates, nitrites, 
and decaying animal and vegetable matters which they 
contain. 

141. Ammonium Compounds of the Soil. — The am- 
monium compounds in a soil are usually less in amount j 
than the nitrates and nitrites. The sources are rain 
water and the organic matter of the soil. The am- 
monium compounds are all soluble and readily undergo 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES I3I 

fixation. See Chapter VI. They cannot accumulate 
in arable soils, because of nitrification and fixation. 
Usually they are to be found in surface well waters. 
In the soil, the ammonium compounds are acted upon 
by nitrifying organisms, and nitrites and nitrates are 
formed. Such compounds as ammonium chloride or 
ammonium carbonate, if present in a soil in excessive 
amounts, will destroy vegetation in a way similar to 
the alkaline compounds in alkaline soils, but in small 
amounts they are beneficial. 

142. Nitrogen in Rain Water and Snow. — Ordinarily 
the nitrogen which is annually returned to the soil in 
the form of ammonium compounds dissolved in rain 
water and snow is equivalent to from 2 to 3 pounds 
per acre. At the Rothamsted Experiment Station the 
average amount for eight years was 3.37 pounds.** 
When a soil is rich in nitrogen the gain from rain 
and snow is only a partial restoration of that which 
has been given off from the soil to the air or lost in the 
drain waters. The principal forms of the nitrogen in 
rain water are ammonium carbonate and nitrates and 
nitrites, present in the air to the extent of about 22 parts 
per million parts of air. 

143. — Ratio of Nitrogen to Carbon in the Organic 
Matter of Soils. — In some soils the organic matter is 
more nitrogenous than in others. In those of the arid 
regions the humus contains from 15 to 20 per cent of 



132 SOILS AND FERTILIZERS 

nitrogen, while in soils from the humid regions there is 
from 4 to 6 per cent.*^ In some soils the ratio of nitro- 
gen to carbon is i to 6, while in others it may be i to 
1 8, or more. That is, in the organic matter of some soils 
there is i part of nitrogen to 6 parts of carbon, while in 
others the organic matter contains i part of nitrogen to 
1 8 parts of carbon. In a soil where there exists a wide 
ratio between the nitrogen and carbon, it is believed the 
conditions for supplying crops with available nitrogen 
are unfavorable. 

144. Losses of Nitrogen from Soils. — When a soil 
rich in nitrogen is cultivated for a number of years ex- 
clusively to grain, there is a loss of nitrogen exceeding 
that removed in the crop, caused by the rapid oxida- 
tion of the organic matter of the soil. Experiments 
show that when a prairie soil of average fertility is 
cultivated continually to grain, for every 25 pounds of 
nitrogen removed in the crop there is a loss of about 
150 pounds due to the destruction of the organic mat- 
ter.!^ In general, any system of cropping which keeps 
the soil continually under the plow results in decreas- 
ing the nitrogen. When a soil is rich in nitrogen the 
greatest losses occur; when poor in nitrogen there is 
relatively less loss. When a soil rich in nitrogen is 
given arable culture, oxidation of the organic matter and 
losses of nitrogen take place rapidly. The longer a 
soil is cultivated, the slower the oxidation of the humus \ 
and relative loss of nitrogen. 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 33 

Dyer has calculated the income and outgo of ni- 
trogen from manured and unmanured plots at the 
Rothamsted Station for a period of fifty years. " Of 
the total 10,000 pounds of nitrogen estimated to have 
been supplied, then, we find (in round numbers) that 
1600 pounds have been recovered in the increased 
crops and that about 2500 pounds are found in the 
surface soil, leaving 5900 (or, in round numbers, 
6000) pounds to be accounted for otherwise. It is 
clear, therefore, in spite of the notable surface ac- 
cumulation, but little of the large quantities of nitrogen 
supplied in the dung and ntot returned in crops is to 
be found in the subsoil. The greater part of it has 
disappeared either as nitrates in the drainage or per- 
haps, and probably largely, by fermentative processes 
yielding free nitrogen." ^^ 

145. Gain of Nitrogen in Soils. — Lawes and Gilbert 
found a gain of nitrogen when land was permanently 
covered with vegetation."** Pastures and meadows 
contain more than cultivated land of similar character. 



Arable land . . 
Barn-field pasture 
Apple-tree pasture 
Meadow . . . 
Meadow . . . 




134 SOILS AND FERTILIZERS 

After deducting the amount of nitrogen in the ma- 
nure added to the meadow land, the annual gain of nitro- 
gen was more than 44 pounds per acre. 

If a soil is properly manured and cropped, the 
nitrogen may be increased. A five-course rotation of 
small grains, clover, and corn (manured) will generally 
leave the soil at the end of the period of rotation in 
better condition as regards nitrogen than at the be- 
ginning. 

At the Minnesota Experiment Station where wheat, 
corn, barley, and oats were grown continuously for 
twelve years, a loss of about 2000 pounds per acre of 
nitrogen was sustained ; from | to |^ of the nitrogen be- 
ing lost in various ways and not utilized as plant food.^^ 
In experiments covering ten-year periods, it, was found 
that the five-year rotations, in which clover formed an 
essential part, resulted in a slight increase in the nitro- 
gen content of the soil, — about 300 pounds per acre in 
excess of that removed in the crops. When timothy 
and non-legumes were substituted for clover, " a loss 
of nitrogen from the soil occurred, but the carbon 
(humus) content was maintained ; the loss of nitrogen 
from the soil only slightly exceeding that removed by 
the crops." ^^ 

It is to be regretted that in the cultivation of large 
areas of land to staple crops, as wheat, corn, and cotton, 
the methods of cultivation followed are such as to de- 
crease the nitrogen content and crop-producing power 
of the soil when this might be prevented. 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 35 

NITRIFICATION 

146. Former Views regarding Nitrification. — The 

presence of nitrates and nitrites in soils was formerly 
accounted for by oxidation. The theory was held that 
the production of nascent nitrogen by the decomposition 
of organic matter caused a union between the oxygen 
of the air and the nitrogen of the organic matter. Fer- 
mentation studies by Pasteur led him to suggest in 1862 
that possibly the formation of nitric acid in the soil 
might be due to fermentation. It was, however, fifteen 
years later before the French chemists, Schlosing and 
Miintz, established the fact that nitrification is pro- 
duced by a living organism. They passed diluted sew- 
age through a glass tube filled with sand to which a 
little lime was added. The first portions of sewage 
contained nitrogen in the form of ammonia, but after a 
number of days nitrates appeared, and the ammonia 
diminished. When the soil was treated with chloro- 
form vapor, nitrates ceased to be formed ; when fresh 
garden soil was added, nitrates again appeared in the 
leachings. The bacteria were destroyed by the chloro- 
form, and the medium was reseeded from the garden 
soil. 

147. Nitrification caused by Micro-organisms. — Nitri- 
fication is the process by which nitrates and nitrites are 
produced in soils by the workings of organisms. Nitri- 
fication results in changing the complex organic nitro- 



136 



SOILS AND FERTILIZERS 



gen of the soil to the form of nitrates or nitrites. 
Broadly speaking, it is the process by which the inert 
nitrogen of the soil is rendered available as crop food. 
The organisms which carry on the work of nitrification 
were first isolated and studied by Winogradsky. 

148. Conditions Necessary for Nitrification are : 

1. Presence of the nitrifying organisms and food for 
them. 

2. A supply of oxygen. 

3. Moisture. 

4. A favorable temperature. 

5. Absence of strong sunlight. 

6. The presence of some basic compound. 

In order to allow nitrification to proceed, all of these 
conditions must be satisfied. The process is frequently 
checked because some of the conditions, as presence of 
a basic compound, are unfulfilled. 



-», 




tf 


• 


• • 


• 




• 


9 ■;-■■ 


<m 


• 
• 
9 


V 




• 


• 
• 


,-■:■». ' 


* 


t 






9 







?.9:-, 


Qi 


"^ 


9 


«„ - 






m 






?? 

^ 


9 

» 


f 




• • • 

• • « 


'':"& 














**^ 


ife;L' 


« 


* 




• 


• • ♦• 


'-,-'* 



Fig. 32. Nitroub Acid Uigaiiisnis. (After Winogradsky.) 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 3/ 

149. Food for the Nitrifying Organisms. — All living 
organisms require food, and one of the food require- 
ments of the nitrifying organism is a supply of phos- 
phates and other minerals. In the absence of phos- 
phoric acid, nitrification cannot take place. The 
change which the phosphoric acid undergoes in serving 




Fig. 33. Nitric Acid Oiganism. (Alter Winogradsky ) 

as food for the nitrifying organism is unknown, but it 
doubtless makes the phosphoric acid more available as 
plant food.^i The principal organic food of the nitrify- 
ing organism is the organic matter of the soil, and it is 
only when organic matter is incorporated with soil that 
it can serve as food for the nitrifying organism. In the 
presence of a large amount of organic matter, as in a 
manure pile, nitrification does not take place. It occurs 
only when the organic matter is largely diluted with 
soil. Under favorable conditions, nitrifying organisms 



138 SOILS AND FERTILIZERS 

may secure all of their food in inorganic forms ; that is, 
nitrification may take place in the absence of organic 
matter, provided the proper mineral food be supplied. 
When growth under such conditions takes place the 
organisms assimilate carbon from the combined carbon 
of the air, and produce organic carbon compounds. An 
organism, working in the absence of sunlight and un- 
provided with chlorophyll, may construct organic com- 
pounds containing nitrogen and designated bacterial 
protein.** Nitrification in the absence of nitrogenous 
organic matter is of too limited a character to supply 
growing crops with all of their available nitrogen. For 
general crop production the organic matter of the soil 
is the source of the nitrogen which undergoes the nitri- 
fication process, and which furnishes food for the nitrify- 
ing organisms. 

150. Oxygen Necessary for Nitrification. — The second 
requirement for nitrification is an adequate supply of 
oxygen. The nitrifying organism belongs to that class 
of ferments (aerobic) which requires oxygen for exist- 
ence. Oxygen is present as one of the elements in the 
final product of nitrification as calcium nitrate, Ca(N03)2. 
In the absence of oxygen, nitrification is checked. 
When soils are saturated with water, the process can- 
not go on for want of oxygen. The formation of a 
hard, dry crust in soils also checks nitrification. Cultiva- 
tion, particularly of clay soils, favors nitrification by 
increasing the supply of oxygen in the soil. 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 39 

151. Moisture Necessary for Nitrification. — Nitrifica- 
tion cannot take place in a soil deficient in moisture ; 
as in all fermentation processes, moisture is necessary 
for the chemical changes to occur. In a very dry time 
nitrification is arrested for want of water. Water is as 
necessary to the growth and development of the living 
organism which carries on the work of nitrification as 
it is to the life of a plant of higher order. 

152. Temperatures Favorable for Nitrification. — The 

most favorable temperatures for nitrification are between 
12° C. (54° F.) and 37° C. (99° F.). It may take place 
at as low a temperature as 3° or 4° C. (37° and 39° F); 
at 50° C. (122° F.) it is feeble ; while at 55° C. (130° F.) 
there is no action.** In northern latitudes nitrification 
is checked during the winter, while in southern latitudes 
this change takes place throughout the entire year. As 
a result, many soils in southern latitudes contain less 
nitrogen than soils in northern latitudes where forma- 
tion and leaching of nitrates are checked by climatic 
conditions. Crops which require their nitrogen early 
in the growing season are frequently placed at a dis- 
advantage because there is less available nitrogen in 
the soil at that time than later. 

153. Strong Sunlight checks Nitrification. — Nitrifica- 
tion cannot take place in strong sunlight ; it prevents 
the action of all organisms of this class. In fallow land 
there is no nitrification at the surface, but immediately 



140 SOILS AND FERTILIZERS 

below where the sunlight is excluded by the surface 
soil it is most active. In a corn field it is more active 
than in a compacted fallow field. 

154. Base -forming Elements Essential for Nitrification. 

— The presence of some base-forming element to com- 
bine with the nitric acid produced is a necessary con- 
dition for nitrification, and for this purpose calcium 
carbonate and sodium and potassium compounds are 
particularly valuable. The absence of alkaline salts is 
one of the frequent causes of non-nitrification. In acid 
soils the process is checked for the want of proper 
basic material. The organisms which carry on the 
work cannot exist where there are strong acids or 
alkalies, consequently in such soils nitrification cannot 
take place. 

155. Nitrous Acid Organisms. — There are at least 
two nitrifying organisms in the soil : one produces 
nitrates and the other nitrites or nitrous acid. It has 
been shown that the nitrification process takes place in 
two stages : first nitrites are produced by the nitrous 
organism, and then the process is completed by the 
nitric organism. Warington says that " both organ- 
isms are present in the soil in enormous numbers, and 
the action of the two organisms proceeds together, as 
the conditions are favorable to both." As a result 
of the workings of the nitrous acid organism, nitrites 
are formed, and these are acted upon by the nitric acid 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES I4I 

organism and changed into nitrates. Nitrites exist in 
soils as transition products, the amount present in fer- 
tile soils being less than one part per million of soil. 

156. Ammonia-producing Organisms. — There are also 
present in the soil organisms which have the power 
of producing ammonia from proteid bodies. The am- 
monium compounds produced are acted upon by the 
nitrifying organisms and readily undergo nitrifica- 
tion.^^' ^^ When oxidation of the protein is rapid, nitro- 
gen may be Hberated and lost. 

157. Denitrification is just the reverse of the nitri- 
fication process, and is the result of the workings of 
a class of organisms which feed upon the nitrates, 
forming free nitrogen which is liberated as a gas. One 
of the conditions for denitrification is absence of air, 
as these organisms belong to the anaerobic class. De- 
nitrification occurs in soils saturated with water, and 
where the soil is compacted so that air is practically 
excluded.*'' ^^ 

158. Number and Kinds of Organisms in Soils. — In 

addition to the micro-organisms which carry on the 
work of nitrification, denitrification, and ammonification, 
there are a great many others, some of which are bene- 
ficial while others are injurious to crop growth. It has 
been estimated that in a gram of an average sample of 
soil there are from 60,000 to 500,000 beneficial and 
injurious micro-organisms.''^ There are produced from 



142 SOILS AND FERTILIZERS 

many crop residues, by injurious ferments, chemical 
products which may be destructive to crop growth. 
Flax straw, for example, when it decays in the soil, 
forms chemical products which are destructive to a 
succeeding flax crop. 

A moist soil, rich in organic matter, and containing 
various salts, may form the medium for the propagation 
of many classes of organisms. Sewage-sick soils, clover- 
sick soils, and flax-diseased lands are all the result of 
bacterial diseases. Many of the organisms which are 
the cause of such diseases as typhoid fever and cholera 
may propagate and develop in a moist soil under certain 
conditions, and then find their way through drain water 
into surface wells, and cause these diseases to spread. 

159. Products formed by Soil Organisms. — In con- 
sidering the part which micro-organisms take in plant 
growth, as well as in all similar processes, there are two 
important phases : (i) the action of the organism itself, 
and (2) the chemical action of the product of the or- 
ganism. In the case of nitrification, the action of the 
organism brings about a change in the composition of 
the organic matter of soils producing nitric acid, which 
is merely a product formed as a result of the action of 
the organism. The nitric acid then acts upon the soil, 
producing nitrates. In soils rich in organic matter the 
fermentation changes, which take place during humifi- 
cation, result in the production of acid products. This 
is simply the result of the action of the ferments. The 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES I43 

acids then act upon the soil bases and produce humates 
or organic salts. In many fermentation changes there 
is first the production of some chemical compound, and 
then the action of this compound upon other bodies. In 
rendering plant food available, as in humification and 
nitrification, it is the final and not the first product of 
the organism, which is of value as plant food. 

160. Inoculating Soils with Organisms. — In growing 
leguminous crops on soils where they have never before 
been produced, it has been proposed to supply the 
essential organisms which assist the crops to obtain 
their nitrogen. For example, if clover is grown on new 
land, the soil may not contain the organisms which 
assist in the assimilation of nitrogen and which are 
present in the root nodules of the plant. If these 
organisms are supplied, better conditions for growth 
exist. Some soils are benefited by inoculation, while 
others are not. Frequently the failure successfully to 
grow legumes is due to other causes, as poor seed, poor 
physical condition of the soil, lack of mineral plant 
food, and adverse climatic conditions rather than to a 
lack of the necessary nitrogen fixing-bacteria.^^ 

In old soils where the process of nitrification is 
feeble, it has been proposed to inoculate the soils with 
more active forms of bacteria so as to make the inert 
humus nitrogen more available as plant food. In order 
to secure the best results from inoculation, suitable 
food must be supplied for the organisms, and any ad- 



144 SOILS AND FERTILIZERS 

verse condition, as excess of acids or alkalies, must 
be corrected. Most soils contain the requisite organ- 
isms, but frequently they are unable to do their work 
because of unfavorable conditions, as the presence of 
injurious matter or the lack of cultivation or food. 
For the production of legumes, inoculation of the soil is 
often beneficial. The commercial production and dis- 
tribution of the organisms forming the nodules on the 
roots of clover and other leguminous crops, and which 
cause fixation of atmospheric nitrogen, was first pro- 
posed and inaugurated by Nobbe.^* The method of in- 
oculation consists in first multiplying the organisms 
in nutritive substances, and then sprinkhng seeds with 
the diluted solution. Inoculation with soil from a field 
where clover or lupines have previously been grown has 
also been successful, particularly in reclaiming sandy 
waste lands where mineral fertilizers containing potash 
and phosphates are used to furnish these elements, 
while the more expensive nitrogen is acquired indirectly 
from the air through the clover. Soils in a high state 
of productiveness are not usually in need of inoculation 
as they already contain all the essential soil organisms. 
Moore's method of distributing the nitrogen-fixing organ- 
isms of legumes in the form of cotton cultures has been 
investigated by a number of experiment stations and 
found inefficient.^'' 

161. Loss of Nitrogen by Fallowing Rich Lands. — 

Summer fallowing; creates conditions favorable to nitri- 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES I45 



fication. A fallow is beneficial to a succeeding crop 
because of the nitrogen which is rendered available. 
If a soil is rich in nitrogen and lime, summer fallow- 
ing causes the production of more nitrates than can be 
retained in the soil. The crop utilizes only a part of 
the nitrogen rendered available, the rest being lost by 
drainage, ammonification, and denitrification. Hence 
the available nitrogen is increased while the total nitro- 
gen is greatly decreased.^ 



Soil before 
Fallowing 



Soil after 
Fallowing 



Total nitrogen . 
Soluble nitrogen 



0.154 
0.002 



0.142 
0.004 



The gain of 0.002 per cent of soluble nitrogen was 
accompanied by a loss of 0.012 per cent of total nitro- 
gen. For every pound of available nitrogen there was 
a loss of six pounds. Bare fallowing of land for an 
entire year should not be practiced, except occasionally 
to destroy weeds or insects, as it results in permanent 
injury to the soil. A short period of fallow and the 
practice of green manuring with leguminous crops both 
enrich the soil with humus and nitrogen, and improve 
the physical properties. 



162. Influence of Plowing upon Nitrification, — In a 
rich soil containing the necessary alkaline matter, nitrifi- 
cation goes on very rapidly. This is one reason why 



146 SOILS AND FERTILIZERS 

shallow plowing on new breaking gives better results 
than deep plowing. Deep plowing at first causes nitri- 
fication to take place to such an extent that the crop is 
over-stimulated in growth, due to an excess of available 
nitrogen. Deep plowing and thorough cultivation aid 
nitrification. The longer a soil has been cultivated, the 
deeper and more thorough must be the cultivation. 

Early fall plowing leaves more available nitrogen at 
the disposal of the crop than late fall plowing. Nitrifi- 
cation takes place only near the surface. Hence when 
late spring plowing is practiced there is brought to the 
surface raw nitrogen, while the more active nitrogen has 
been plowed under, and is beyond the reach of the young 
plants when they require the most help in obtaining food. 
The various methods of cultivation, as deep and shallow 
plowing, spring and fall plowing, and surface cultivation, 
have as much influence upon the available nitrogen 
supply of crops as upon the water supply. The saying 
that cultivation makes plant food available is particu- 
larly true of the element nitrogen, the supply of which 
is capable of being increased or decreased to a greater 
extent than that of any other element. 

NITROGENOUS MANURES 

163. Sources of Nitrogenous Manures. — The materials 
used for enriching soils with nitrogen, to promote crop 
growth, may be divided into two classes: (i) organic 
nitrogenous manures, (2) mineral nitrogenous manures. 



NITROGEN, NITRIFICATION,- NITROGENOUS MANURES 1 4/ 

Each of these classes has a different vakie as plant 
food, and in fact there are marked differences in fertili- 
zer value between materials belonging to the same class. 
The nitrogenous organic materials used for fertiUzing 
purposes are : dried blood, tankage, meat scraps and 
flesh meal, fish offal, cottonseed meal, and leguminous 
crops, as clover and peas. The nitrogen in these sub- 
stances is principally in the form of protein. When 
peat and muck are properly used they also may be 
classed among the nitrogenous manures. The mineral 
nitrogenous manures are nitrates, as sodium nitrate, and 
ammonium salts, as ammonium sulphate. 

164. Dried Blood. — This is obtained by drying the 
blood and debris from slaughterhouses. Frequently 
small amounts of salt and slaked lime are mixed with 
the blood. It is richest in nitrogen of any of the 
organic manures. When thoroughly dry it may contain 
14 per cent of nitrogen. As usually sold, it contains 
from 10 to 20 per cent of water, and has a nitrogen 
content of from 9 to 13. Dried blood contains only 
small amounts of other fertilizer elements ; it is strictly 
a nitrogenous fertilizer, readily yielding to the action of 
micro-organisms and to nitrification. On account of its 
fermentable nature, it is a quick-acting fertilizer, and is 
one of the most valuable of the organic materials used as 
manure. It gives the best returns on an impoverished 
soil to aid crops in the early stages of growth, before 
the inert nitrogen of the soil becomes available. Dried 



148 SOILS AND FERTILIZERS 

blood may be applied as a top dressing on grass land, 
and it is also an excellent form of fertilizer for many 
garden crops ; but it should not be placed in direct con- 
tact with seeds, as it will cause rotting, nor should it be 
used in too large amounts. Three hundred pounds per 
acre is as much as should be appHed at one time. When 
too much is used losses of nitrogen may occur by leach- 
ing and by denitrification. It is best applied directly to 
the soil as a top dressing in the case of grass, or near 
the seeds of garden crops, and not mixed with unslaked 
lime or wood ashes, but each should be used separately. 
As all plants take up their nitrogen in the early stages 
of growth, nitrogenous fertilizers as blood should be ap- 
plied before seeding or soon after. An application of 
dried blood to partially matured garden crops will cause 
a prolonged growth and very late maturity. 

Storer gives the following directions for preserving 
any dried blood produced upon farms.^^ " The blood 
is thoroughly mixed in a shallow box with 4 or 5 times 
its weight of slaked lime. The mixture is covered with 
a thin layer of lime and left to dry out. It will keep if 
stored in a cool place, and may be applied directly to 
the land or added to a compost heap." 

The price per pound of nitrogen in the form of dried 
blood can be determined from the cost and the analysis 
of the material. A sample containing 9 per cent of nitro- 
gen and selling for $28 per ton is equivalent to 15-55 
cents per pound for the nitrogen (2000x0.09=180. 
).oo-7- 180= 15.55 cents). 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES I49 

165. Tankage is composed of refuse matter, as bones, 
trimmings of hides, hair, horns, hoofs, and some blood. 
The fat and gelatin are, as a rule, first removed by sub- 
jecting the material to superheated steam. This mis- 
cellaneous refuse, after drying, is ground and some- 
times mixed with a little slaked lime to prevent rapid 
fermentation. 

Tankage contains less nitrogen but more phosphoric 
acid than dried blood. Owing to its miscellaneous na- 
ture, it is quite variable in composition, as the following 
analyses of tankage from the same abattoir at different 
times show : ^* 



Moisture 
Nitrogen 
Phosphoric acid 



per cent 



First 
Year 



10.5 

5-7 
12.2 



Second 
Year 



9.8 

7.6 

10.6 



Third 

Year 



10.9 

6.4 

II.7 



As a general rule, tankage contains from 5 to 8 per 
cent of nitrogen and from 5 to 12 per cent of phos- 
phoric acid. It is much slower in its action than dried 
blood, and supplies the crop with both nitrogen and 
phosphoric acid. Tankage is a valuable form of fer- 
tilizer for garden purposes. It may also be used as 
a top dressing on grass lands, or spread broadcast on 
grain lands. It is best to apply the tankage, when pos- 
sible, a few days prior to seeding, and it should not 
come in contact with seeds. Two hundred and fifty 



150 SOILS AND FERTILIZERS 

pounds per acre is a safe dressing, and when there is 
sufficient rain to ferment the tankage, 400 pounds per 
acre may be used. A dressing of 800 pounds in a dry 
season would be destructive to vegetation. On impov- 
erished soil more may be used than on soils which are 
for various reasons out of condition. The cost of the 
nitrogen as tankage is determined from the composi- 
tion and selling price. If tankage containing 7 per 
cent of nitrogen and 12 per cent of phosphoric acid is 
selling for $32 per ton, what is the cost of the nitrogen 
per pound ? The market value of phosphoric acid, in 
the form of bones, should first be ascertained. Sup- 
pose bone phosphoric acid is selling for 4 cents per 
pound. The phosphoric acid in the ton of tankage 
would then be worth 1^9.60, making the nitrogen cost 
^22.40. The 140 pounds of nitrogen in the ton of fer- 
tilizer would be worth $22.40, or 16 cents per pound. 
In eastern markets the price of tankage is usually higher 
than near the large packing houses of the West. 

166. Flesh Meal. — The flesh refuse from slaughter- 
houses is sometimes kept separate from the tankage 
and sold as flesh meal, the fat and gelatin being first 
removed and used for the manufacture of glue and 
soap. Flesh meal is variable in composition and may 
be very slow in decomposing. It contains from 4 to 8 
per cent or more of nitrogen, with an appreciable amount 
of phosphoric acid. Occasionally it is used for feeding 
poultry and hogs, and cattle to a limited extent. The 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES I5I 

fertilizer value of the dung is nearly equivalent to the 
original value of the meal. 

167. Fish Scrap. — The flesh of fish is very rich in 
nitrogen."*^ The offal parts, as heads, fins, tails, and intes- 
tines, are dried and prepared as a fertilizer. Some species 
of fish which are not edible are caught in large numbers 
to be used for this purpose. In seacoast regions, fish fer- 
tilizer is one of the cheapest and best of the nitrogenous 
manures. It is richer in nitrogen than tankage or flesh 
meal, and in many cases equal to dried blood. It read- 
ily undergoes nitrification and is a quick-acting fertilizer. 

168. Seed Residues. — Many seeds, as cottonseed and 
flaxseed, are exceedingly rich in nitrogen. When the oil 
has been removed, the flaxseed and cottonseed cake are 
proportionally richer in nitrogen than the original seed. 
This cake is usually sold for cattle food, but occasionally 
is used as fertiUzer. It contains from 6 to 7 per cent of 
nitrogen, and compares fairly well in nitrogen content 
with animal bodies. Cottonseed cake and meal are not 

i so quick acting as dried blood, but when used in south- 

] em latitudes a Httle time before seeding, the nitrogen 

{ becomes available for crop purposes. Oil meals, as 

j cottonseed and linseed, containing a high per cent of 

( oil, are much slower in decomposing than those which 

i contain but little oil. It is better economy to feed the 

i cake to stock and use the manure than to apply the cake 

: directly to the land. Occasionally, however, cottonseed 



152 SOILS AND FERTILIZERS 

meal has been so low in price that its use as a fertilizer 
has been admissible. 

A ton of cottonseed meal, costing $20 and containing 
2 per cent of phosphoric acid and 7 per cent of nitro- 
gen, would be equivalent to 13.1 cents per pound for 
the nitrogen, which is frequently cheaper than purchas- 
ing some other nitrogenous fertilizer. 

169. Leather, Wool Waste, and Hair are rich in nitro- 
gen, but on account of their slowness in decomposing 
are unsuitable for fertilizer purposes. When present in 
fertilizers they give poor field results. 

170. Available Nitrogen. — One of the methods em- 
ployed to detect, in fertilizers, the presence of inert 
forms of nitrogen, as leather, is to digest the material in 
prepared pepsin solution. ^*^ Substances like dried blood 
are nearly all soluble in the pepsin, while leather and other 
inert forms are only partially so. The solubihty of the 
organic nitrogen in pepsin solution determines, to a great 
extent, the value of the material as a fertilizer.^^ 



Dried blood . . . 
Cottonseed meal 
Ground dried fish . 
Tankage .... 
Hoof and horn meal 
Leather .... 



Per Cent of Nitrogen 

Soluble in Prepared 

Pepsin Solution 




NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 53 

Some of the organic forms of nitrogen readily undergo 
nitrification and become available as plant food, while 
other forms are inactive. Vegetation tests show that 
from 60 to 75 per cent of the nitrogen of dried blood, 
tankage, cottonseed meal, and fish meal are available as 
plant food the year they are used as fertilizer. The 
available nitrogen of fertilizers includes nitrates and 
ammonium salts and such forms of organic matter as 
readily undergo nitrification. Potassium permanganate 
with and without sodium hydroxide is also employed 
as a solvent for available nitrogen. ^^ 

171. Peat and Muck. — Peat and muck are rich in 
nitrogen which is in an insoluble form and is with diffi- 
culty nitrified. When mixed with lime and stable 
manure, particularly liquid manure, fermentation is 
induced and a valuable manure produced. Muck and 
peat should be dried and sun-cured, and then used as 
absorbents in stables. Peat differs from muck in being 
fibrous. If the muck is acid, lime (not quicklime) should 
be used with it in the stable, as directed under farm 
manures. When easily obtained, muck is one of the 
cheapest forms of nitrogen. 

Composition of Dry Muck Samples^ 



Nitrogen 
Per Cent 



Marshy place, producing hay 
Marshy place, dry in late summer 
Old lake bottom 



2.21 
2.01 
1.81 



154 SOILS AND FERTILIZERS 

172. Leguminous Crops as Nitrogenous Manures. — 
The frequent use of leguminous crops for manurial pur- 
poses is the cheapest way of obtaining nitrogen. When 
the crop is not removed from the land but is plowed 
under while green, the practice is called green manur- 
ing. This does not enrich the land with any mineral 
material, but results in changing inert plant food to 
humate forms. Green manuring with leguminous crops 
should take the place of bare fallow, as its effects upon 
the soil are more beneficial. With green manuring, 
nitrogen is added to the soil, while with bare fallow there 
is a loss of nitrogen. Leguminous crops, as clover, peas, 
crimson clover, and cowpeas, should be made to serve 
as the main source of the nitrogen for crop production. 
A good crop of clover will return to the soil over 200 
pounds of nitrogen per acre. 

173. Sodium Nitrate. — The nitric nitrogen most 
frequently met with in commercial forms is sodium 
nitrate, commonly known as Chili saltpeter. It is a 
natural deposit found extensively in Chili, Peru, and 
the United States of Colombia. Various theories have 
been proposed to account for these deposits, but it is 
difficult to determine just how they have been formed.^*' 
The commercial value of nitrogen in fertilizers is regu- 
lated mainly by the price of sodium nitrate, which, when 
pure, contains 16.49 P^^ cent of nitrogen. Commer- 
cial sodium nitrate is from 95 to 97 per cent pure. 
An ordinary sample contains about 16 per cent of 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 55 

nitrogen and costs from $50 to $60 per ton, making 
the nitrogen worth from 15 to 18 cents per pound. 
Sodium nitrate is the most active of all the nitrogenous 
manures. It is soluble and does not have to undergo 
the nitrification process before being utilized by crops. 
On account of its extreme solubility it should be ap- 
plied sparingly, for it cannot be retained in the soil. 
As a top dressing on grass, it will respond by impart- 
ing a rich green color. It may be used at the rate of 
250 pounds per acre, but a much lighter application will 
generally be found more economical. Sodium nitrate 
should not be used when heavy dressings of farm 
manure are appHed, as denitrification may result from 
such a practice. In small amounts it is the fertilizer 
most frequently resorted to when the forcing of crops 
is desired, as in early market gardening. Its use for 
fertilizing horticultural crops has become equally as ex- 
tensive as for general farm crops. Excessive amounts, 
however, may produce injurious results. Sodium nitrate 
stimulates a rank growth of dark green foliage and 
retards the maturity of plants, but when properly used 
is one of the most valuable of the nitrogenous ferti- 
lizers. 

174. Ammonium Sulphate. — Ammonium sulphate is 
obtained as a by-product in the manufacture of illu- 
minating gas and is extensively sold as a fertilizer. It 
usually contains about 20 per cent of nitrogen, equiv- 
alent to 95 per cent of ammonium sulphate, the re- 



156 SOILS AND FERTILIZERS 

maining 5 per cent being moisture and impurities. 
Ammonium sulphate is not generally considered the 
equivalent of sodium nitrate, as it is believed it must 
undergo nitrification before being utilized as plant 
food. It is, however, a valuable form of nitrogen. Ex- 
periments show that plants may utilize ammonia directly 
without nitrification processes first taking place.'^^ The 
statements regarding the use of sodium nitrate apply 
equally well to the use of ammonium sulphate. Am- 
monium chloride and ammonium carbonate are not 
suitable for fertilizers on account of their destructive 
action upon vegetation. 

175. Calcium Nitrate and Cyanamid, Ca(N03).2 and 
CaCNg. — The nitrogen of these compounds is obtained 
from the free nitrogen of the air by electrical processes. 
Calcium nitrate is made by treating Hme with nitric acid 
resulting from the oxides of nitrogen produced in the 
air by electrical action. It is a valuable form of nitrogen 
fertilizer. Calcium cyanamid is made by heating together 
coal and lime in an electrical furnace through which a 
current of nitrogen gas, obtained from the air, is passed. 
Experiments with calcium cyanamid as a fertilizer show 
that the nitrogen undergoes nitrification and becomes 
available as plant food.^^ It is claimed that these com- 
pounds of nitrogen Ca(N03)2 and CaCN2, in which the 
nitrogen is obtained from the air, will eventually be pro- 
duced at such a low cost as to permit their extensive use 
as fertilizers. 



NITROGEN, NITRIFICATION, NITROGENOUS MANURES 1 5/ 

176. Nitrogen and Ammonia Equivalent of Fertilizers. 

— Nitrogenous fertilizers are sometimes represented 
as containing a certain amount of ammonia instead of 
nitrogen. Fourteen-seventeenths of ammonia is nitro- 
gen, and if a fertilizer contains 2.25 per cent ammonia, 
it is equivalent to 1.85 per cent of nitrogen. To convert 
NHg results to an N basis, multiply by 0.823. 

177. Purchasing Nitrogenous Manures. — In purchas- 
ing a nitrogenous manure, the special purpose for which 
it is to be used should always be considered. Under 
some conditions, as forcing a crop on an impoverished 
soil, sodium nitrate is desirable. Under other conditions, 
tankage, cottonseed cake, or some other form of nitro- 
gen may be better. There is annually expended in pur- 
chasing nitrogenous fertilizers a large amount of money 
which could be expended more economically if the 
science of fertilizing were given a more careful study, 
and if a larger share of the nitrogen for crop pur- 
poses were obtained indirectly from the air through the 
agency of legumes. The uses of nitrogenous fertilizers 
for special crops and the testing of soils to determine 
any deficiency in nitrogen are discussed in Chapters 
X and XI, which treat of commercial fertilizers and the 
food requirements of farm crops. 



CHAPTER V 

FARM MANURES 

178. Variable Composition of Farm Manures. — The 
term ' farm manure ' does not designate a product of 
definite composition. Manure is the most variable in 
chemical composition of any of the materials produced 
on the farm. It may contain a large amount of straw, 
in which case it is called coarse manure ; or it may con- 
tain only the soUd excrements and a little straw, the 
liquid excrements being lost by leaching ; then again 
it may consist of the droppings of poorly fed animals, 
or of the mixed excrements of different classes of well- 
fed animals. 

The term * stable manure ' has been proposed for that 
product which contains all of the solid and liquid excre- 
ments with the necessary absorbent, before any losses 
have been sustained. ^^ The term 'barnyard manure' is 
restricted to that which accumulates around some barns 
and farmyards, and is exposed to leaching rains and the 
drying action of the sun. 

179. Average Composition of Manures. — The soHd 
excrements of animals contain from 60 to 85 per cent 
of water ; when mixed with straw, and the liquid ex- 
crements are retained, the mixed manure contains 

158 



FARM MANURES 



159 



about 75 per cent of water. The nitrogen varies from 
0.4 to 0.9 per cent, 'according to the nature of the food 
and the extent to which other factors have affected the 
composition. In general, animals consuming liberal 




-4. 2.1:3. 

Fig. 34. Average Composition of Fresh 

Manure. 

I. Nitrogen. 2. Phosphoric acid. 

3. Potash. 4. Mineral matter. 




Fig. 35. Manure after Six 
Months' Exposure. 



amounts of coarse fodders produce manure with a 
higher per cent of potash than of phosphoric acid. 
This is because the potash in the food exceeds the 
phosphoric acid. Farm manures also contain lime, 
magnesia, and other minerals present in plants and 
designated as essential ash elements. The average 
composition of mixed stable manure is as follows : 



Nitrogen, N . . . 
Phosphoric acid, P^O^ 
Potash, K„0 . . . 



Average 
Per Cent 



0.50 

0-35 
0.50 



Range 
Per Cent 



0.4 to 0.8 
0.2 to 0.5 
0.3 to 0.9 



i6o 



SOILS AND FERTILIZERS 



In calculating the amount of fertility in manures, it 
is more accurate to compute the value from the food 
consumed and the conditions under which the manure 
has been produced, than to use figures expressing aver- 
age composition. 

180. Factors which influence the Composition and 
Value of Farm Manure. — 

I. Kind and amount of absorbents used. 
11. Kind and amount of food consumed. 

III. Age and kind of animals. 

IV. Methods employed in collecting, preserving, and 
utilizing the manure. 

Any one of the above, as well as many minor fac- 
tors, may influence the composition and value of farm 
manures. 

181. Absorbents. — The absorbent generally used is 
straw. Wheat straw and barley straw have about the 
same manurial value ; oat straw is more valuable than 
either. The average composition of straw and other 
absorbents is as follows : 



Nitrogen . . . 
Phosphoric acid 
Potash . . . . 



Straw 
Per Cent 



0.40 
0.36 
0.80 



Leaves 
Per Cent 



0.6 

0-3 
0-3 



Peat 
Per Cent 



Sawdust 
Per Cent 



O.I 
0.2 
0.4 



When a large amount of straw is used the percentage 
amounts of nitrogen and phosphoric acid are decreased, 



FARM MANURES l6l 

while the per cent of potash is slightly increased. Saw- 
dust and loam both make the manure more dilute. Dry- 
peat makes the. manure richer in nitrogen. The ab- 
sorptive power of these different materials is about as 
follows : 1* 



Per Cent of 
Water Absorbed 



Fine cut straw 
Coarse uncut straw 

Peat 

Sawdust .... 



30.0 
18.0 
60.0 

45.0 



The proportion of absorbents in manure ranges from 
a fifth to a third of the total weight of the manure. 

182. Use of Peat and Muck as Absorbents. — Because 

of the high content of nitrogen in peat and the power 
which it possesses when dry of absorbing water, it is 
a valuable material to use as an absorbent in stables. 
As previously stated, peat is slow to decompose, but 
when mixed with the liquid manure it readily yields to 
fermentation, particularly if a Httle land plaster or marl 
be used in the stable along with the peat. Peat has 
high absorptive power for gases as well as for liquids, 
and when used the sanitary condition of stables is im- 
proved and the air is rendered particularly free from 
foul odors. 



l62 



SOILS AND FERTILIZERS 



RELATION OF FOOD CONSUMED TO MANURE PRODUCED 

183. Bulky and Concentrated Foods. -r- The more con- 
centrated and digestible the food consumed, the more 
valuable is the manure. Coarse bulky fodders always 
give a large amount of a poor quality of manure. For 
example, the manure from animals fed on timothy hay 
and that from animals fed on clover hay and grain 
show a wide difference in composition. The dry matter 
of timothy hay is about 55 per cent digestible. From 
a ton of timothy hay there is about 790 pounds of dry 
matter in the manure. The nitrogen, phosphoric acid, 
and potash in the food consumed are nearly all returned 
in the manure, except under those conditions which will 
be noted. The manure from a ton of mixed feed, as 
clover and bran, is smaller in amount but more concen- 
trated than that produced from timothy. In a ton of 
timothy and in a ton of mixed feed (1500 lbs. clover, 
500 lbs. bran) there are present: 



Timothy 
Lbs. 



Mixed Feed 
Lbs. 



Nitrogen . . 
Phosphoric acid 
Potash . . . 



25.0 

9.0 

40.0 



40.0 
24.0 
30.0 



The nitrogen, phosphoric acid, and potash of these 
two rations are retained in the animal body in dissimi- 
lar amounts, 10 per cent more of these elements being 



FARM MANURES I63 

retained from the more liberal ration, due to more 
favorable conditions for growth. Because of this fact 
there is present in the manure from the mixed feed one 
half more nitrogen, and two and one half times as much 
phosphoric acid, as in the manure from the timothy 
hay, which, free from bedding, contains about 790 
pounds of indigestible matter, while the manure from 
the mixed feed contains 760 pounds, the mixed ration 
being more digestible. If both manures contain the 
same amount of absorbents, the manure from the ton 
of mixed clover and bran will weigh slightly less, 
but contain more fertility than that from the timothy 
hay. 

The value of manure can be accurately determined 
from the composition of the food consumed and the 
care which the manure has received. Only a small 
amount of the nitrogen in the food is permanently 
retained in the body. The larger portion is used for 
repair purposes, the nitrogen of the tissues which 
have been renewed being voided as urea in the 
liquid excrements. Some of the nitrogenous com- 
pounds of the food are utilized for the production 
of fat, in which case the nitrogen is voided in the 
excrements. The fact that but little of the nitrogen 
and mineral matter of the food, under most condi- 
tions, is retained in the body is shown by the in- 
vestigations of Lawes and Gilbert upon the compo- 
sition of the flesh added to animals while undergoing 
the fattening process.^^ 



164 



SOILS AND FERTILIZERS 



Increase during Fattening 





Water 


Dry 

Matter 


Fat 


Nitrogenous 
Matter 


Ash 


Ox 

Sheep .... 
Pig .... 


24.6 
20.1 
22.0 


75-4 

79-9 
78.0 


66.2 
70.4 

71-5 


7.69 

7-13 
6.44 


1.47 
2.^6 
0.06 



The results of numerous digestion experiments show 
that when the food undergoes digestion only from 5 
to 15 per cent of the nitrogen is, as a rule, retained 
in the body. The nitrogen of the food is utilized 
largely to replace that which has been required for 
vital functions ; it enters the body, undergoes digestion 
changes, is utilized for some vital function, and is then 
voided in the excrements. 

The digestion of food has been compared to the 
combustion of fuel : the undigested products of the 
solid excrements represent the ashes, and the urine 
represents the volatile products. When wood is burned 
the nitrogen is converted into volatile products. When 
food is digested and utilized by the body the digestible 
nitrogen is mainly converted into urea, while the indi- 
gestible nitrogen is voided in the dung. In the solid 
and liquid excrements of animals from 80 to 95 per 
cent of the nitrogen, phosphoric acid, and potash of the 
food consumed is present. t. 

184. Comparative Composition of Solid and Liquid Ex- 
crements. — In composition the liquid excrements differ 



FARM MANURES 



165 



from the solids in having a much larger amount of 
nitrogen and less phosphoric acid.^ 





Water 


Nitrogen 


Phosphoric Acid 


Potash 




a 

-a " 

u 
CAIPh 


'3 " 

JfL, 


c 


U) C 
-O V 

'3 " 

.H"S 


P Solids 
^ Per cent 


•a u 
'3 " 

.2-5 


c 

■3 S 


Cows . . 


76 


89.0 


0.50 


1.20 




0.30 


Horses . 


84 


92.0 


0.30 


0.86 


0.25 




O.IO 


Pigs . . 


80 


97.0 


0.60 


0.80 


0.45 


0.12 


0.50 


Sheep 


58 


86.5 


0.75 


1.40 


0.60 


0.05 


0.30 



The nitrogen in the food consumed influences the 
amount of water in the manure. As a rule, a highly- 
concentrated nitrogenous ration produces a higher per 
cent of water than a well-balanced ration. There is 
but little phosphoric acid in the liquid excrements of 
horses and cows, while that of sheep and swine contains 
appreciable amounts. 

The liquid manure is more constant both in compo- 
sition and amount than the solid excrements. This 
fact may be observed from the following table, which 
gives the composition of the solid and liquid excre- 
ments of hogs when fed on different amounts of 
grain, ^" 

The nitrogenous waste matter in the urine is nearly 
the same whether an animal be gaining or losing in flesh, 
and hence it is, the urine is more constant in composi- 
tion and quantity than the solid excrements. 



1 66 



SOILS AND FERTILIZERS 







Solid 


Liquid 




Kind of Food Daily 


Excrements 


Excrements 


Lbs. 


c 

3 
o . 







he u 
u 

i ^ 

go; 


1^ a(^ 


9^ 


Barley and shorts .... 


8 


0.57 


0.72 


2.05 


0.06 


6 


Barley 


4 


043 


0.70 


2.06 


0.16 


5h 


Corn and shorts .... 


2.V 


0.80 




2.65 


0.20 


61 


Corn 


i| 


0.82 


0.89 


2.05 


0.29 



(In each experiment the amount of liquid excrement was 4 pounds.) 



The amount and composition of the solid excre- 
ments vary with the amount and kind of food con- 
sumed. If the food is indigestible, the solid excrements 
contain a larger part of the nitrogen as indigestible 
protein. When an animal is supplied with the proper 
food for all purposes, normal conditions exist, and the 
amount of nitrogen voided in the liquid and solid 
excrements is equal to that supplied in the food con- 
sumed, except in the case of growing and milk-pro- 
ducing animals. 

Experiments at the Rothamsted Station show that 
from 57 to 79 per cent of the total nitrogen in the 
food of farm animals is voided in the liquid excrements, 
and from 16 to 22 per cent is voided in the solids. 
Nearly all of the mineral elements of the food are 
voided in the excrements, less than 4 per cent being 



FARM MANURES 



167 



retained in the body; in the case of milk cows about 10 
per cent of the ash of the food is recovered in the milk. 

185. Manurial Value of Foods. — The manurial value 
of a fodder is determined from the amount and com- 
mercial value of the nitrogen, phosphoric acid, and 
potash present in the fodder. A ton of clover hay, for 
example, contains 35 pounds of nitrogen, 14 pounds of 



Timothy hay . 
Clover hay . 
Wheat straw 
Oat straw . . 
Wheat . . . 
Oats .... 
Barley .... 
Rye .... 
Flax .... 
Corn .... 
Wheat shorts . 
Wheat bran 
Linseed meal . 
Cottonseed meal 
Milk .... 
Cheese 

Live cattle . . 
Potatoes . . . 
Butter . . . 
Live pigs . . 



Nitrogen 

N 

Lbs. 



25 

35 
1 1 
12 
45 
33 
40 
42 
87 
- 32 
48 

54 
100 

130 

ID 
90 

53 
7 
I 

40 



Phosphoric Acid 
P2O5 
Lbs. 



9 

14 

4 

4 

20 

16 

18 

20 

32 

14 

31 

52 

35 

35 

3 

23 

37 

3 

I 

17 



Potash 
K,0 
Lbs. 



40 

30 
12 
18 
12 
II 
II 
13 
14 



30 
25 
56 

3 
5 
3 
II 
I 
3 



l68 SOILS AND FERTILIZERS 

phosphoric acid, and 30 pounds of potash. When the 
nitrogen is worth 16 cents per pound, the phosphoric 
acid 6 cents, and the potash 5 cents, the clover hay has 
a manurial value of 1^7.94 per ton, Lawes and Gilbert 
estimate that 80 per cent of the fertility in fodders is, 
as a rule, returned in the manure. 

In the preceding table are given the pounds of nitro- 
gen, phosphoric acid, and potash per ton of some farm 
products.^^ 

186. Commercial Value of Manures. — When the value 
of farm manure is calculated on the same basis as com- 
mercial fertihzers, it will be found that stable manure 
is worth from $2 to $3.50 per ton. The value of the 
increased crops resulting from its use varies with con- 
ditions. Farm manures favorably influence the yield of 
crops for a number of years. As for example, a dress- 
ing of 8 tons of manure will make average prairie land 
yield upwards of 20 bushels per acre more corn the 
first year, 5 bushels more wheat the second year, and 8 
bushels or so more of other grains the third year, with 
slightly increased yields in subsequent years, all due 
to the original application of the manure. It is often 
necessary to apply farm manure in order to secure a 
stand of clover, which enriches the soil with nitrogen. It 
sometimes takes from two to three years for the manure 
entirely to repay the cost of its application. Its influence 
is felt, however, for a much longer time. In calculating 
the value of farm manure, the returns from its use for a 



FARM MANURES I 69 

number of years must be considered and also its in- 
fluence in permanently increasing the value of the land. 

It is sometimes stated that the phosphoric acid and 
potash in stable manure is not so soluble as that in 
commercial fertilizers, and consequently is worth, less. 
While not so soluble in the form of manure, it fre- 
quently happens that the phosphoric acid and potash 
in the commercial fertilizers become, through fixation 
processes, less soluble when mixed with the soil than 
the same elements in stable manure. 

Stable manure is valuable not only for the fertiHty con- 
tained but also because it makes the inert plant food of 
the soil more available and exercises such a favorable in- 
fluence on the water supply of crops ; hence it is justi- 
fiable to assign the same, if not a higher, value to the 
elements in well-prepared farm manures as to those in 
commercial fertilizers. 

INFLUENCE OF AGE AND KIND OF ANIMAL 

187. Manure from Young and from Mature Animals. 

— The manure from older animals is somewhat more 
valuable than that from young animals, even when fed 
the same kind of food. This is because more of the 
phosphoric acid and nitrogen are retained in the body 
of a young animal. It is not so much a difference in 
digestive power as a difference in retentive power. In 
older animals the proportion of new nitrogenous tissue 
produced is much less than in young animals, and more 



170 SOILS AND FERTILIZERS 

of the nitrogen of the food is used for repair purposes 
and subsequently voided in the manure, while with 
young animals more of the nitrogen is retained for the 
construction of new muscular tissue. 

When an animal is neither gaining nor losing in flesh, 
and is not producing milk, an equihbrium is established 
between the nitrogen in the food supply and the nitro- 
gen in the manure, and practically all of the nitrogen 
of the food is returned in the manure.^" 

188. Cow Manure. — A milch cow when fed a bal- 
anced ration will make from 60 to 70 pounds of solid 
and liquid manure a day, of which 20 to 30 pounds are 
liquid. The solid excrement contains about 6 pounds 
of dry matter. When a cow is fed clover hay, corn 
fodder, and grain, about half of the nitrogen of the food 
is in the urine, about one fourth in the milk, and the re- 
mainder in the solid excrement. Hence, if the solid 
excrement only is collected, but a quarter of the nitro- 
gen of the food is recovered; while if both solids and 
liquids are utilized, three quarters of the nitrogen is 
secured. Cow manure is extremely variable in compo- 
sition and is the most bulky of any manure produced by 
domestic animals. A well-fed cow will produce about 
80 pounds of manure per day, including absorbents. 

189. Horse Manure. — Horse manure contains less 
water than cow manure, and is of a more fibrous na- 
ture, doubtless due to the horse possessing less power 



FARM MANURES I7I 

for digesting cellulose material. Horse manure readily 
ferments and gives off ammonia products. When the 
manure becomes dry, fire-fanging results, due to rapid 
fermentation followed by the growth of fungous bodies, 
and there is a heavy loss of nitrogen. Horse manure 
is sometimes considered of but little value. This is 
because it so readily deteriorates that when used it has 
often lost much of its nitrogen by fermentation. When 
mixed with cow manure, both are improved, the rapid 
fermentation of the horse manure is checked, and at 
the same time the cow manure is improved in texture. 
It is estimated that horses void about three fifths of 
their manure in the stable. A well-fed horse at ordi- 
narily hard work produces 50 pounds per day, of 
which about one fourth is urine. A horse produces 
nearly 6 tons of manure per year in the stable. If 
properly preserved and used, it is valuable and quick- 
acting ; but if allowed to ferment and leach, it gives 
poor results. 

190. Sheep Manure. • — Sheep produce a small amount 
of concentrated manure, containing less water than that 
of any other domestic animal. It readily ferments and 
is a quick-acting fertilizer. When combined with horse 
and cow manure the mixture ferments more slowly. 
Because of the small amount of water it contains, sheep 
manure is very concentrated in composition. It is val- 
uable for general gardening purposes and whenever a 
concentrated, quick-acting manure is desired. 



1/2 SOILS AND FERTILIZERS 

191. Hog Manure. — Hog manure is not constant in 
composition on account of the varied character of the 
food consumed. The manure from fattening hogs 
which are well fed compares favorably in composition 
and value with that produced by other animals. It 
contains a high per cent of water, and, like cow ma- 
nure, may be slow in decomposing. On account of 
containing so much water, losses by leaching readily 
occur. From a given weight of grain, pigs produce 
less dry matter in the manure than do sheep or cows. 
The liquid excrements of well-fed hogs are rich in ni- 
trogen, containing, on an average, about 2 per cent. 
The solids when leached, fermented, and deprived of 
the liquid excrements have little value as fertilizer. 

192. Hen Manure. — Like all other farm manures, 
hen manure is variable in composition. The nitrogen 
is mainly in the form of ammonium compounds, making 
it a quick-acting fertilizer. When fowls are well fed 
the manure contains about the same amount of nitro- 
gen as that of sheep. Hen manure readily ferments 
and if not properly cared for losses of nitrogen, as 
ammonia, occur. It is not advisable to mix with it 
hard wood ashes or ordinary lime, because the ammo- 
nia is so readily liberated by alkaline compounds. The 
value of hen manure is due to its being a quick-acting 
fertiUzer rather than to its containing a large amount of 
fertility. A hen produces about a bushel of manure 
per year. 





farm manures 
Composition of Hen Manure 


173 




Per Cent 


Water 


57-50 
1.27 
0.82 


Nitrogen 


Phosphoric acid 
Potash . . . 






28 







193. Mixing of Solid and Liquid Excrements. — The 

solid and liquid excrements together make a well-bal- 
anced manure. Urine alone is not a complete manure, 
as it is deficient in phosphoric acid and other mineral 
matter. The solid excrement and the urine, when 
combined with soil, readily undergo nitrification. The 
nitrogen in the solid excrement is in the form of indi- 
gestible protein and is rendered available more slowly 
as plant food. Land dressed with leached manure re- 
ceives an unbalanced fertilizer deficient in nitrogen but 
fairly well supplied with mineral matter and may fail to 
respond because of the unbalanced character of the 
manure. A large amount of fertility is often lost 
through poor and leaky stable floors. When the floors 
and trenches are made of cement, better sanitary condi- 
tions prevail and losses of fertility are prevented. 
The mixing of the solid and liquid excrements and 
waste bedding should be accomplished in the stable 
trenches. 

194. Volatile Products from Manure. — Fermentation 
of manure in stables results in the production of a large 



174 SOILS AND FERTILIZERS 

number of volatile compounds and in loss of manurial 
value. When urea ferments, ammonium carbonate, a 
volatile product, results ; and where the proteids of ma- 
nure ferment, ammonia is formed, which combines with 
the carbon dioxide, always present in stables in Uberal 
amounts as a product of respiration, to form ammonium 
carbonate, a volatile compound. When the stable at- 
mosphere becomes charged with ammonium carbonate, 
some of it is deposited on the walls of the stable, 
forming a white coating. The white coating found 
on harnesses and carriages stored in poorly ventilated 
stables is ammonium carbonate. Accumulations of 
manure in the stable and poor ventilation are the condi- 
tions favorable to its production. 

195. Human Excrements. — The use of human excre- 
ments as manure is sometimes advised, and in some 
countries they are extensively so utilized. When fresh, 
they may contain a high per cent of nitrogen and phos- 
phoric acid ; but when fermented, a loss of nitrogen has 
occurred. Heiden estimates looo pounds a year of 
excrements per person, containing $2.25 worth of fertil- 
ity.^^ For sanitary reasons, human excrements should 
be used as manure with great care, and it is doubtful, 
with the abundance and cheapness of plant food, 
whether the practice is advisable. About 1840 Leibig 
expressed tbe fear that the essential elements of plant 
food would accumulate in the vicinity of large cities and 
be wasted, and that in time there would be a decline in 



FARM MANURES 



175 



fertility due to this cause.^*^ Many political economists 
shared the same fear. Since that time the fixation of 
atmospheric nitrogen through the agency of leguminous 
crops has been discovered, extensive beds of sodium 
nitrate, phosphate rock, and Stassfurt salts have been 
utilized, and larger areas of more fertile soil have been 
brought under cultivation, so that it is not now so 
essential to devise means for utilizing human excre- 
ments as manure. 

THE PRESERVATION OF MANURE 

196. Leaching. — Leaching of manure is the greatest 
source of loss. Experiments by Roberts show that 
when horse manure is thrown in a loose pile and sub- 
jected to the joint action of leaching and weathering it 
may lose in six months nearly 60 per cent of its most 
valuable fertiHzing constituents. The results of these 
experiments are tabulated as follows: ^^ 



Gross weight 
Nitrogen . . 
Phosphoric acid 
Potash . . . 
Value per ton 



April 25 
Lbs. 



4000.00 
19.60 
14.80 
36.00 



Sept. 28 
Lbs. 



1730.00 

7-79 

7-79 

8.65 

$1.06 



Loss 
Per Cent 



57 
60 

47 
76 



Cow manure, on account of its more compact nature, 
does not leach so readily as horse manure. A similar 



176 



SOILS AND FERTILIZERS 



experiment with cow manure, conducted at the same 
time, showed the following losses : 



April 25 


Sept. 28 


Loss 


Lbs. 


Lbs. 


Per Cent 


10,000 


5 


[25 


49 


47 




28 


41 


32 




26 


19 


48 




44 


8 


$2.29 


$1 


.60 


— 



Gross weight . 
Nitrogen . . 
Phosphoric acid 
Potash . . . 
Value per ton 



When mixed cow and horse manure was compacted 
and " placed in a galvanized iron pan with a perforated 
bottom " for six months, the losses were as follows : 





March 29 


Sept. 30 


Loss 




Lbs. 


Lbs. 


Per Cent 


Gross weight 


226.00 


222.00 





Nitrogen 


1.04 


1. 01 


3-2 


Phosphoric acid .... 


0.61 


0.58 


47 


Potash 


1.20 


0.43 


35-0 


Value per ton .... 


$2.38 


$2.16 





197. Losses by Fermentation. — When rapid fermen- 
tation takes place in manure, appreciable losses of 
nitrogen may occur. When the manure is well com- 
pacted and the pile is so constructed as to prevent rapid 
circulation of air through it, losses are reduced to the 
minimum. Experiments show that when leaching is 
prevented, the loss of nitrogen by fermentation of mixed 



FARM MANURES 



177 



manure is very small. Under poor conditions losses by- 
fermentation may exceed 15 per cent. Hen manure, 
sheep manure, and horse manure are the most ferment- 
able, particularly when fungous growths and molds are 
formed. When extreme conditions, as excessive mois- 
ture, are followed by drought and high temperature, 
then the greatest losses occur. 



198. Different Kinds of Fermentation. — The large 
number of organisms present in manure all belong to 
one of two classes: (i) aerobic, or (2) anaerobic. The 
aerobic ferments require an abundant supply of air in 
order to carry on their 
work. When deprived 
of oxygen, they become 
inactive. The anaero- 
bic ferments require 
the opposite condition. 
They become inactive 
in the presence of oxy- 
gen and can thrive only ^^^^ ^^- Fermentation of Manure. 

when air is excluded. In the center of a well-constructed 
manure pile anaerobic fermentation occurs, while on 
the surface aerobic fermentation is active. The anaer- 
obic ferments prepare the way for the action of the 
aerobic. When aerobic fermentation is completed, the 
organic matter is converted into water, carbon dioxide, 
ammonia, and allied gases, and these are lost. Conse- 
quently, anaerobic fermentation is the most desirable. 




178 SOILS AND FERTILIZERS 

The bacterial content of the soil is greatly increased 
by the use of farm manures, and also food is supplied 
to the organisms already in the soil, many of which take 
an important part in rendering plant food available. 

199. "Water Necessary for Fermentation. — In order to 
produce the best results in fermenting manure, water is 
necessary; for if the manure becomes too dry, abnormal 
fermentation takes place. Water is always beneficial on 
manure so long as leaching is prevented, for it encour- 
ages anaerobic fermentation by excluding the air. An 
excess of water, such as falls on manure piles from the 
eaves of buildings, is more than is required for good 
fermentation. During a dry time it is beneficial to water 
the compost pile. 

200. Heat produced during Fermentation. — During 
active fermentation of horse and sheep manure a tem- 
perature of 175° F. may be reached by the fermenting 
mass. Ordinarily, however, the temperature of the 
manure pile ranges from 110° to 130° F. The highest 
temperature is near the surface, where fermentation is 
most rapid. The temperature of fermentation may be 
sufficiently high to cause spontaneous combustion, if the 
manure is mixed with litter. 

201. Composting Manure may improve its Quality. — 

Composting manure so that leaching and rapid fermen- 
tation do not take place may improve its quality, mak- 



FARM MANURES 



179 



ing it more concentrated. Pound for pound, composted 
manure is richer in plant food than fresh manure, be- 
cause, if properly cared for, nearly all of the nitrogen, 
phosphoric acid, and potash of the original manure are 
present in smaller bulk. A ton of composted manure is 
obtained from about 2800 pounds of stable manure. 
Composting is sometimes resorted to in order to destroy 
obnoxious weed seeds. 



Nitrogen . . 
Phosphoric acid 
Potash . . . 



Fresh 


Composted 


Manure 


Manure 


Per Cent 


Per Cent 


0.50 


0.60 


0.28 


0-39 


0.60 


0.80 



In composting manure it should be the aim to induce 
anaerobic fermentation by excluding the air and retain- 
ing the water. This can be accomplished best by using 
mixed manure and making a compact pile, capable of 
shedding water. The compost pile should be shaded to 
secure better conditions for fermentation. If the pile 
becomes offensive, a little earth on the surface will 
absorb the odors. 



202. Use of Preservatives. — The use of preservatives, 
as gypsum and kainit, has been -recommended to prevent 
fermentation losses. Opinions differ as to the value of 
this practice. Moist gypsum, when it comes in contact 



l8o SOILS AND FERTILIZERS 

with ammonium carbonate, produces ammonium sul- 
phate, a non-volatile compound, 

(NH4)2C03 + CaSO^ = (NH4)2S04 + CaCOg. 

Gypsum when used should be at the rate of about 
one half pound per day for each animal.^^ Experiments 
show that it prevents a loss of 5 per cent of the nitro- 
gen of horse manure. It has no action on the feet of 
animals, and so may with safety be sprinkled in the 
stalls. When it is necessary to use gypsum as a fertilizer, 
it is advantageous to use it in stables. It is not advis- 
able to use lime in any other form than the sulphate. 
Unslaked lime will decompose manure and liberate am- 
monia. Neither kainit nor gypsum should be used when 
manure is exposed to the leaching action of rains. Pre- 
servatives cannot be made to take the place of care in 
handling manure ; they should be used only when the 
manure receives the best of care. 

203. Manure produced in Sheds and Box Stalls. — 

Manure produced under cover, as in sheds and box 
stalls, is of superior quality. Losses by leaching are 
thus avoided, the manure is compacted by the tramping 
of the animals, the solid and liquid excrements are more 
evenly mixed with the absorbents, and the conditions 
are favorable for anaerobic fermentation. By no other 
system is there such a large percentage of the fertihty 
recovered. Manure from well-fed cattle, when collected 



FARM MANURES l8l 

and prepared in a covered shed, will have about the 
following composition : 



Water . . . 
Nitrogen . . 
Phosphoric acid 
Potash . . . 



Per Cent 


70.00 


0.90 


0.60 


0.70 



Manure produced under cover has greater value than 
when cared for in any other way. Experiments by 
Kinnard show that such manure produced 4 tons more 
potatoes per acre than pile manure, while 1 1 bushels 
more wheat per acre were obtained on land which had 
the previous year received the covered manure than on 
land which received the uncovered manure.^^ Experi- 
ments at the Ohio Station show that stall manure gives 
a larger crop yield than yard nianure.^^ 

THE USE OF MANURE 

204. Direct Hauling to Fields. — It is always desirable, 
whenever conditions allow, to draw the manure directly 
to the field and spread it, rather than to allow it to ac- 
cumulate about barns or in the barnyard. When taken 
I directly to the field from the stable no losses by leach- 
! ing occur, and the slight losses from fermentation and 
j volatilization of the ammonia are more than compensated 
\ for by the benefits derived from the action of the fresh 



102 SOILS AND FERTILIZERS 

manure upon the soil. When manure undergoes fer- 
mentation in the soil, as previously stated, it combines 
with the mineral matter of the soil and produces humates. 
The practice of hauling the manure directly to the field 
and spreading it with a manure spreader is the most eco- 
nomical way of handling it, as the manure is thus evenly 
spread, and larger crop returns are secured from the 
lighter and more frequent applications. 

With scant rainfall composting the manure before 
spreading is often necessary, but with liberal rainfall it 
is not essential. On a loam soil, a direct application of 
stable manure is more advisable than on heavy clay or 
Hght sandy soil. In the case of sandy soils there is fre- 
quently an insufficient supply of water properly to fer- 
ment the manure. Manure on heavy clay land sometimes 
fails to show any beneficial effect the first year because 
of the slow rate of decomposition, but the beneficial 
effects are noticeable the second and third years. 

When conditions will not permit farm manure to be 
hauled directly to the field and spread, it should be 
stored in covered manure sheds, so as to prevent leach- 
ing and injurious fermentation. 

205. Coarse Manure Injurious. — The application of 
coarse leached manure may cause the soil to be so 
open and porous as to affect the water supply of the 
crop, by introducing below the surface soil a layer of 
straw, and thus breaking the capillary connection with 
the subsoil. Coarse manure and shallow spring plowing ' 



FARM MANURES 



183 



are sometimes injurious, where fine or well-composted 
manure and fall plowing would be beneficial. Trouble 
resulting from the use of coarse manure may be due to 
its being allowed to leach before it is used, so that it 
does not readily ferment in the soil. 

206. Manuring Pasture Land. — In regions where 
manure decomposes slowly, it is sometimes advisable to 
use it upon pasture land as a top dressing. The manure 
encourages growth of the grass, so that it appropriates 
plant food otherwise lost ; it also acts as a mulch, pre- 
venting excessive evaporation. Then when the pasture 
land is plowed and prepared for a grain crop it contains a 
better store of both water and available plant food. The 
manuring of pasture lands is one of the best ways of utiliz- 
ing manure when trouble arises from slow decomposition. 



207. Small Manure Piles Undesirable. — It is some- 
times the custom to make a number of small manure 
piles in fields. This is a poor practice, for it entails 
additional ex- , ,,,,,,, r- ,v ^/^ ,f.i,.s,u,>un /n^ 

pense later m Mi^IIi^ulj^^ 
spreading the t^'^-^"' '- - — -"--'- *:r^^ra^- 
manure, and 
the small piles 
are usually 
constructed in 

such a way Fig. 37. Manured Land. 

that heavy losses occur, so the manure, when finally 




1 84 



SOILS AND FERTILIZERS 



ilvift«(S\rir/fi 1^ 



spread, is not uniform in composition. Oats grown on land 
manured in tliis way presented an uneven appearance. 

, ;| f, „. //.,,! .'//- .^M'/ There were 
^^^Ju^-4x^.,j.4-J-^._.U-,..^,.<--^ small patches, 

thrifty and 
overfed, cor- 
responding to 
the places 
formerly occu- 

FlG. 38. Unmanured Land. • i i 1 

pied by the 
manure piles, while large areas of half-starved oats 
miffht be observed. 




208. Rate of Application. — The amount of manure 
that should be appUed depends upon the nature of the 
soil and the crop. On loam soils intended for general 
truck purposes, heavier applications may be made than 
when grain is raised. For general farm purposes, 8 
tons per acre are usually sufficient. It is better 
economy to make frequent and light applications than 
heavier ones at long intervals. When manure is 
spread frequently the soil is kept in an even state 
of fertility, and losses by percolation, denitrification, and 
ammonification are prevented. Too often the manure 
is not evenly distributed about the farm ; fields adjacent 
to stables are heavily manured, while those at a distance 
receive none. 

For growing garden crops, 20 tons and more per 
acre are sometimes used. It is better, however, not 



FARM MANURES 185 

to use stable manure in excess for trucking, but to 
supplement it with special fertilizers as the crops may 
require. Soils which contain a large amount of cal- 
cium carbonate will not become acid from farm manure, 
and hence admit of more frequent and heavier applica- 
tions than soils which are deficient in this compound. 
The lime aids fermentation and nitrification. Some- 
times a judicious combination of farm manure and 
commercial fertilizers can be made that will prove 
more economical than farm manure alone. 

209. Crops Most Suitable for Manuring. — Soils which 
contain a low stock of fertiUty admit of manuring for 
the production of almost any crop. Soils well stocked 
with plant food, like some of the western prairie soils, 
which are in need of manure mainly for its physical 
action, will not allow its direct use on all crops. On 
a prairie soil of average fertility a heavy application 
of manure may cause wheat and other grain crops to 
lodge. When manure cannot be applied directly to 
a crop, it may be used advantageously on a preced- 
ing crop and the land thus be brought into good 
condition for the crop that will not bear direct ma- 
nuring. Manure never injures corn by causing too 
rank a growth, and wheat may follow corn which 
has been manured with but little danger of loss from 
lodging. 

On some soils stable manure cannot be used for 
growing sugar beets ; on others it does not seem to exer- 



l86 SOILS AND FERTILIZERS 

cise an injurious effect. Tobacco is injured as to quality 
by manure. Flax, tobacco, sugar beets, and wheat, 
which should not receive heavy direct applications, all 
require manuring of the preceding crops. When in 
doubt as to the crop on which to use the manure, it is 
always safe to apply it to corn, and then to follow with 
the crop which would have been injured by its direct 
application. 

That coarse, leached manure may cause trouble in a 
dry season, and well-rotted manure may cause grain to 
lodge, are not valid reasons for manure being wasted as 
it frequently is in western farming, by being burned, 
thrown away in streams, used in making roads, or for 
filling up low places. 

210. Comparative Value of Forage and Manure. — 

The manure from a given amount of grain or fodder 
always gives better results than if the food itself were 
used directly as manure. The manure from a ton of 
bran will give better returns than if the bran itself 
were used. This is because so little of the fertility 
is lost during the process of digestion, and the action 
of the digestive fluids upon the food makes the manure 
more readily available as a fertilizer than the food 
which has not passed through any fermentation pro- 
cess. It is better economy to use products as linseed 
meal and cottonseed meal for feeding stock, and then 
take good care of the manure, than to use the mate- 
rials directly as fertilizer. 



FARM MANURES 187 

211. Lasting Effects of Manure. — No other manures 
make themselves felt for so long a time as farm ma- 
nures. In ordinary farm practice an application of 
stable manure will visibly affect the crops for a num- 
ber of years. At the Rothamsted Experiment Station, 
records have been kept for over fifty years as to the 
effects of manures upon soils. In one experiment, 
farm manure was used for twenty years and then dis- 
continued for the same period. It was observed that 
when its use was discontinued there was a gradual 
decline in crop-producing power, but not so rapid as 
of plots where no manure had been used. The manure 
applied during the twenty-year period made itself felt 
for an ensuing twenty years. 

212. Comparative Value of Manure produced on Two 
Farms. — The fact that there is a great difference in 
the composition and value of manures produced on 
different farms may be observed from the following 
examples : 

On one farm lo tons of timothy are fed. The 
liquid manure is not preserved and 25 per cent of the 
fertility is leached out of the solid excrements, while 5 
per cent of the nitrogen is lost by volatilization. It is 
estimated that half of the nitrogen and potash of the 
food is voided in the urine. On account of the scant 
amount and poor quality of the food no milk or flesh 
is produced. 

On another farm 7.5 tons of clover hay and 2.5 tons 



l88 SOILS AND FERTILIZERS 

of bran are fed. The liquid excrements are collected 
and the manure is taken directly to the field and 
spread. It is estimated that 20 per cent of the nitro- 
gen and 4 per cent of the phosphoric acid and potash 
are utilized for the production of flesh and milk. 

The comparative value of the manure from the two 
farms is as follows : 

Farm No. i 

In 10 Tons Timothy 
Lbs. 

Nitrogen 250 

Phosphoric acid 90 

Potash 400 

Loss in Urine 

250 -;- 2 = 125 lbs. nitrogen 
400 -=- 2 = 200 lbs. potash 

Loss by Leaching 

125 X 0.30 = 37.50 lbs. nitrogen 
90 X 0.25 = 22.50 lbs. phosphoric acid 
200 X 0.25 = 50 lbs. potash 

Total Loss 
Lbs. Per Cent 

Nitrogen 162.5 65 

Phosphoric acid . . , . . . . 22.5 25 

Potash 250.0 62 

Present in Final Product 
Manure from i Ton Timothy 
Lbs. 

Nitrogen 8.75 

Phosphoric acid 6.75 

Potash 15.00 

Relative money value $1.00 



FARM MANURES I 89 

Farm No. 2 

In 10 Tons Mixed Feed 
Lbs. 

Nitrogen 400 

Phosphoric acid 240 

Potash 300 

Loss, Sold in Milk and Retained in Body 
Lbs. Per Cent 

Nitrogen, 400 x 0.20 80 20 

Phosphoric acid, estimated ... 10 4 

Potash 12 4 

Present in Final Product 

Manure from i Ton Feed 

Lbs. 

Nitrogen 32.0 

Phosphoric acid 23.0 

Potash 29.0 

Relative money value $3.80 

213. Summary of Ways in which Stable Manure 
may be Beneficial. — Farm manures act upon soils 
chemically, physically, and bacteriologically. 
(a) Chemically : 

1. By adding new stores of plant food to the soil. 

2. By combining with the soil, forming humates, and 
rendering the inert mineral plant food more available. 

3. By raising the temperature of the soil, as the re- 
sult of oxidation. 

(d) Physically : 

1. By making the soil darker colored. 

2. By enabling soils to retain more water and to give 
it up gradually to growing crops. 



190 SOILS AND FERTILIZERS 

3, By improving the tilth of sandy and clay soils. 

4. By preventing the denuding effects of heavy wind 
storms. 

(c) Bacteriologically : 

1. By increasing the number of soil organisms. 

2. By promoting fermentation changes. 

3. By supplying food to the organisms which assist 
in rendering plant food available. 



CHAPTER VI 

FIXATION 

214. Fixation, a Chemical Change. — When a fer- 
tilizer is applied to a soil, chemical reaction takes 
place between the soil and the fertilizer. There is 
a general tendency for the soluble matter of fertilizers 
to undergo chemical change and become insoluble. 
This process is known as fixation. If a solution of 
potassium chloride be percolated through a column of 
clay, the filtrate will contain scarcely a trace of potas- 
sium chloride, but instead calcium and other chlorides. 
The element potassium of the potassium chloride has 
been replaced by the element calcium present in the 
soil, and as a result of this exchange of base elements 
an insoluble compound of potash is formed. Indepen- 
dent of chemical action, a small amount of soluble salts 
are absorbed physically by soils and retained by molec- 
ular force. Absorption is a physical property of soils, 
while fixation is due to a chemical change. 

215. Fixation due to Zeolites. — It has been shown by 
experiments, particularly those of Way and Voechler,^^ 
that fixation is due mainly to zeolitic silicates. Sandy 
soils containing but little clay have only feeble power 
of fixation. Clay soils when digested with hydrochloric 

191 



192 SOILS AND FERTILIZERS 

acid to remove the zeolitic silicates lose their power of 
fixation. The fixation of potassium chloride and the 
liberation of calcium chloride may be illustrated by the 
following reaction : 

Zeolite Zeolite 

AI2O3 
K.,0 




^■(Si02)^-H.20 + 2KC1 = ^ ^ 
etc. 



;r(Si02)x-H20 + CaCla. 



216. Humus may cause Fixation. — Also other com- 
pounds of the soil, as humus and calcium carbonate, 
take an important part in fixation. In the case of 
humus, a union occurs between the minerals in the 
fertihzer and the organic acids formed from the decay 
of the humus in the soil, resulting in the production of 
humates. 

217. Variations in Fixative Power of Soils. — All soils 
do not possess the power of fixation to the same extent. 
Heavy clays have the greatest fixative power, while 
sandy soils have the least. As a general rule, soils of 
high fertility show good fixative power. Hence it is 
that a fertilizer, after being applied to a soil, may be 
entirely changed in composition, so that the plant feeds 
on the chemical products formed, rather than on the 
original fertilizer. . 

218. Fixation of Phosphates. — The phosphates of 
fertilizers readily undergo fixation by combination with 



FIXATION 193 

the iron and aluminum compounds of soils, forming in- 
soluble phosphates. Experiments show that in a loam 
soil from 2000 to 8000 pounds per acre of phosphoric 
acid may undergo fixation. Drainage waters contain 
only traces of phosphates. At the Rothamsted Experi- 
ment Station the plots receiving an annual dressing of 
phosphates for fifty years contained 83 per cent of the 
surplus fertilizer, half of which was in available forms 
soluble in one per cent citric acid.^^ 

219. Fixation of Potash. — The potash compounds of 
fertilizers readily undergo fixation, the sodium and cal- 
cium of the soil being replaced by the potassium of the 
fertihzer. Drainage waters contain larger amounts of 
sodium than of potassium compounds, due to greater in- 
solubility of the potash of the soil. Fixation of potash 
occurs mainly in the surface soil, where it is held in 
forms insoluble in water, a portion being soluble in 
dilute acids. 

220. Nitrates cannot undergo Fixation. — Nitrogen in 
the form of nitrates or nitrites cannot undergo fixation. 
This is because all of the ordinary forms of nitrates are 
soluble. If potassium nitrate be added to a soil, calcium 
or sodium nitrate will be obtained as the soluble com- 
pound. The potassium undergoes fixation, but the ni- 
trate radical does not. Chlorides also are incapable of 
undergoing fixation, because all of the chlorides found 
in soils are soluble. 



194 SOILS AND FERTILIZERS 

221. Fixation of Ammonia. — Ammonium compounds 
readily undergo fixation, particularly in the presence of 
clay. (See experiment No. 17.) The ammonium radi- 
cal, NH4,like potassium, is capable of replacing soil 
bases. After undergoing fixation, the ammonium com- 
pounds readily yield to nitrification (see Section 156), 
hence they serve as a temporary but important form of 
insoluble nitrogen. The general tendency of the nitro- 
gen compounds of the soil is to pass from insoluble to 
soluble forms through processes of decay, and to resist 
fixation changes. 

222. Fixation may make Plant Food Less Avail- 
able. — If a very heavy dressing of potash or phosphate 
fertilizer be applied to a heavy clay soil, what is not 
utilized the first few years may undergo fixation to such 
an extent that part becomes unavailable as plant food. 
It is not well to apply unnecessarily heavy dressings of 
fertilizers at long intervals because of fixation. It is 
always best to make light and frequent applications. 

223. Fixation, a Desirable Property for Soils. — If it 
were not for the process of fixation, soils in regions of 
heavy rains would soon become sterile. When the 
plant food has become insoluble, it is retained in the 
soil. That which undergoes fixation is, as a rule, in an 
available condition or may readily become so by cultiva- 
tion unless the soil be one of unusual composition. The 
process of fixation regulates the supply of plant food in 



FIXATION 



195 



the soil. Many fertilizers, if they did not undergo this 
process, would be injurious to crops, for there would be 
an abnormal amount of soluble alkahne or acid com- 
pounds which would be destructive. When the process 




Fig. 39. Plants grown in Normal Soil. 

of fixation takes place, it removes, to a great extent, 
injurious water-soluble salts, particularly when the reac- 
tion is one of union rather than replacement. Then 
the plant is free to render soluble its own food in quan- 
tities and at times desired. 
j Farm manures and commercial fertilizers alike un- 
; dergo the process of fixation and, in studying ferti- 
I lizers, their action upon the soil and the products of 
I fixation are matters of prime importance. 



196 



SOILS AND FERTILIZERS 



224. Soil Solution. — Soil water obtained by leaching 
soils is an exceedingly dilute solution of various mineral 
salts and organic compounds. Through rock disinte- 
gration, mineral matter is rendered soluble, but the pro- 
cess of fixation prevents accumulation in the soil solution 




Fig. 40. 



Plants grown in Sand and watered with Leachings (Soil Solu- 
tion) from Soil as used in Fig. 39. 



of compounds of such elements as potassium and phos- 
phorus. As a result of disintegration and fixation, 
numerous chemical changes take place in the soil, and 
the soil solution is an important factor in bringing about 
these changes. Many of the phenomena which have 
been studied in connection with solutions in physical 
chemistry take place in the soil. Diffusion, absorption, 
osmotic pressure, and ionization,^^ — disassociation of the 
molecule in solution, — all occur in soils and are due 



FIXATION 197 

largely to the physical and chemical action of the soil 
solution. The soil solution from different soils varies 
with the composition and degree of disintegration of 
the soil particles, and in the same soil at different times 
there are variations in its composition. The soil solution 
is more important as an agent for bringing about chem- 
ical and physical changes in the soil than as a store- 
house of plant food. It is not possible to exhaust a soil 
of all of its water-soluble salts by one or more leachings. 
There appears to be a variable but fairly continuous 
solubility of soil constituents. King has shown that 
soils of high productiveness contain a larger amount of 
soluble salts than soils of low fertility.^" 



CHAPTER VII 



PHOSPHATE FERTILIZERS 




Fig. 41. Oat Plant grown without 
Phosphates. 



225. Importance of Phos- 
phorus as Plant Food. — 

Phosphorus in the form of 
phosphates is one of the 
essential elements of plant 
food. None of the higher 
orders of plants can complete 
their growth unless supplied 
with this element. The il- 
lustration (Fig. 41) shows an 
oat plant which received no 
phosphorus compounds, but 
was supplied with all the 
other elements of plant food. 
As soon as the phosphoric 
acid stored up in the seed 
had been utiHzed, the plant 
ceased to grow, and after a 
few weeks, died of phosphate 
starvation, having made the 
total growth shown in the 
illustration. All crops de- 
mand their phosphorus com- 
pounds at an early stage of 
development. Wheat takes 
198 



PHOSPHATE FERTILIZERS 1 99 

up 80 per cent of its phosphoric acid in the first half of the 
growingperiod,^'^ while clover has assimilated all it requires 
by the time the plant reaches full bloom.^^ Phosphorus 
compounds accumulate, to a great extent, in the seeds 
of grains, and hence, when grain farming is extensively 
followed, are sold from the farm. All crops are very 
sensitive to the absence of phosphoric acid ; an imper- 
fect supply results in the production of light-weight 
grain. The nitrogen and phosphorus are to a great 
extent stored up in the same parts of the plant, par- 
ticularly in the seed, which is richer in both of these 
elements than is any other part. Nitrogen is the chief 
element of protein, while phosphorus is also necessary 
for the formation of some of the phosphorus and ni- 
trogen compounds, as the nucleo-albumins and lecithin. 
Phosphorus aids in the production of the protein com- 
pounds. In speaking of the phosphorus compounds in 
plants and in fertilizers, as well as in soils, the term 
'phosphoric anhydride' or 'phosphorus pentoxide,' P2O5, 
commonly called phosphoric acid, is used. This is be- 
cause phosphorus is an acid-forming element and, as 
already explained, the anhydride of the element is al- 
ways considered instead of the element itself. 

226. Amount of Phosphoric Acid removed in Crops. — 

Grain crops remove about 20 pounds per acre of phos- 
phoric acid; the amount removed by other farm crops 
ranges from 18 to 28 pounds, as will be observed from 
the following table : 



200 



SOILS AND FERTILIZERS 



Wheat, 20 bu. . . 

Straw, 2000 lbs. . . 

Total . . . 

Barley, 40 bu. . . 

Straw, 3000 lbs. . . 

Total . . . 

Oats, 50 bu. . . . 

Straw, 3000 lbs. . . 

Total . . . 

Corn, 65 bu. . . . 

Stalks, 4000 lbs. . . 

Total . . . 

Peas, 3500 lbs. . . 
Red clover, 4000 lbs. 
Potatoes, 150 bu. 

Flax, 15 bu. . . . 

Straw, 1800 lbs. . . 

Total . . . 



Phosphoric Acid 

P2O5 

Per Acre 

Lbs. 



12.5 

7-5 
20.0 

20 

12 

6 

Ts 
18 

4 
22 

25 
28 

20 

15 
3 



227. Amount and Source of Phosphoric Acid in Soils. 

— To meet the demand of growing crops for about 25 
pounds of phosphoric acid per acre, there are present in 
soils from 0.03 to 0.25 per cent. This is equivalent to 
from 1000 pounds and less to 9000 pounds per acre, of 
which, however, only a fraction is available as plant food at 



PHOSPHATE FERTILIZERS 201 

any one time. The availability of the phosphoric acid has 
a great deal to do in determining crop-producing power. 
Many soils contain a large amount of total phosphoric 
acid which has become unavailable, because of poor cul- 
tivation and absence of stable manure and lime to com- 
bine with the phosphates and render them available. 

The phosphates in soils are derived mainly from the 
disintegration of phosphate rock and from the remains 
of animal life. The phosphate deposits found in various 
localities are supposed to have had their origin either 
in the remains of marine animals or sea water highly 
charged with soluble phosphates. These deposits have 
been subjected to various geological and climatic changes 
which have resulted in the formation of soft phosphate, 
pebble phosphate, and rock phosphate.^^ 

228. Commercial Forms of Phosphoric Acid. — The 

sources of phosphate fertilizers are : (i) phosphate rock, 
(2) bones and bone preparations, (3) phosphate slag, and 
(4) guano. With the exception of phosphate slag and 
guano, the prevailing form of phosphorus is tricalcium 
phosphate. Before being used for commercial purposes 
the tricalcium phosphate, which is insoluble and unavail- 
able, is treated with sulphuric acid, which produces mono- 
calcium phosphate, a soluble and available form. 

Ca3(P04)2 + 2 H2SO4 -h 5 H2O = CaH4(P04)2 + H^O + 
2 CaS04, 2 H2O. 

In making phosphate fertilizers from bones or phos- 



202 SOILS AND FERTILIZERS 

phate rock, an excess of the rock is used so there will be 
no free acid in the fertilizer to be injurious to vegetation. 
As stated above, the usual form in which calcium phos- 
phate is found in nature is tricalcium phosphate, 
Ca3(P04)2, and unless associated with organic matter 
or salts which render it soluble, it is of but little value as 
plant food. When tricalcium phosphate is treated with 
sulphuric acid, monocalcium phosphate, Ca.}ri^(F0^)2, is 
formed, which is soluble in water and directly available 
as plant food. When tricalcium and monocalcium phos- 
phate are brought together in a moist condition, dical- 
cium phosphate is produced. 

CagCPO^)., + CaH^CPO^).^ = 2 Ca2H2(P04)2. 

Another form of phosphate of lime, met with in basic 
phosphate slag, is tetracalcium phosphate, (CaO)4P20g. 

229. Reverted Phosphoric Acid. — When mono- and 
tricalcium phosphate react, the product is known as re- 
verted phosphoric acid, which is insoluble in water, but 
is not in such form as to be unavailable as plant food ; it 
is generally considered available. Reverted phosphoric 
acid may also be formed by the action, upon mono- 
calcium phosphate, of iron and aluminum compounds 
present as impurities in the phosphate rock. As it is 
soluble in a dilute solution of ammonium citrate, it is 
sometimes spoken of as citrate-soluble phosphoric acid, 
and is not all equally valuable as plant food because of 
the different phosphate compounds that may be dissolved 



PHOSPHATE FERTILIZERS 203 

by this solvent. Citrate-soluble phosphoric acid may be 
present in an old fertilizer in two forms, — dicalcium 
phosphate and hydrated phosphates of iron and alumi- 
num. 

230. Available Phosphoric Acid. — As applied to fer- 
tilizers, the term 'available phosphoric acid' includes the 
water-soluble and citrate-soluble phosphoric acid. These 
solvents do not, under all conditions, make a sharp dis- 
tinction as to the available and unavailable phosphoric 
acid when it comes to plant growth. Some forms of 
bone which are insoluble in an ammonium citrate solu- 
tion are available as plant food, while some forms of 
aluminum phosphate which are soluble are of but little 
value. The fineness of division of the fertilizer particles 
also greatly influences the availability of the phosphoric 
acid. The terms 'available' and ' unavailable phosphoric 
acid,' as applied to commercial fertilizers, refer to the 
solubility of the phosphates, and, as a rule, the value of 
the phosphates as plant food is in accord with their sol- 
ubility — the more insoluble the less valuable. 

231. Phosphate Rock. — Phosphate rock is found in 
many parts of the United States, particularly in South 
Carolina, North Carolina, Florida, Virginia, and Tennes- 
see. The deposits occur in stratified veins, as well 
as in beds and pockets. There are different types 
of phosphates, as hard rock, soft rock, land pebble, 
and river pebble. The pebble phosphates are found 



204 SOILS AND FERTILIZERS 

either on land or collected in cavities in water courses, 
and are generally spherical masses of variable size. 
Soft rock phosphate is easily crushed, while the hard 
rock requires pulverizing with rock crushers. Phosphate 
rock usually contains from 40 to 70 per cent of calcium 
phosphate, the equivalent of from 17 to 30 per cent 
phosphoric acid. The remaining 30 to 60 per cent is 
fine sand, limestone, alumina, and iron compounds, with 
other impurities, which often render a phosphate un- 
suitable for manufacture into high-grade fertilizer. 

232. Superphosphate. — Pulverized rock phosphate, 
known as phosphate flour, is treated with commercial 
sulphuric acid to obtain soluble monocalcium phosphate. 
The amount of sulphuric acid used is determined by the 
composition of the rock. Impurities as calcium carbon- 
ate and calcium fluoride react with sulphuric acid and 
cause a loss of the acid. Ordinarily, a ton of high-grade 
phosphate rock requires a ton of sulphuric acid. The 
mixing is done in lead-lined tanks. A weighed amount 
of phosphate flour is placed in the tank and the sulphuric 
acid added, through lead pipes, from the acid tower. The 
mixing of the acid and phosphate is done with a mechani- 
cal mixer, driven by machinery. From the mixing tank 
the material is passed into other large tanks, where two 
or three days are allowed for the completion of the 
reaction. The mass is placed in piles to solidify and is 
then ground and sold as superphosphate. In the manu- 
facture of superphosphate, gypsum (CaS04.2H20) is 



PHOSPHATE FERTILIZERS 20$ 

always produced. A ton of superphosphate prepared 
from high-grade rock in the way outlined will contain 
about 40 per cent of Hme phosphate, equivalent to i8 
per cent phosphoric acid. If a poorer quality of rock 
is used, there is a proportionally smaller amount of phos- 
phoric acid. A more concentrated superphosphate is 
known as double superphosphate and is obtained by pro- 
ducing phosphoric acid from the phosphate rock, and 
then allowing the phosphoric acid to act upon fresh por- 
tions of the rock, the reactions being as follows : ^* 

Ca3(P04)2 -h 3 H.2SO4 = 3 CaSO^ + 2 HgCPO^). 
Ca3(POj2 + 4 H3PO4 + 3 H2O = 3[CaH4(P04)2, H^O]. 

The phosphoric acid is separated from the gypsum 
before acting upon the phosphate flour. In this way, 
superphosphate containing from 35 to 45 per cent of 
phosphoric acid is produced. When fertilizers are to be 
transported long distances, this concentrated product is 
preferable. The terms ' acid ' and ' superphosphate ' 
have been generally used to designate the first product 
resulting from the action of sulphuric acid upon phos- 
phate rock or bones, and the term ' double superphos- 
phate ' to mean the concentrated product formed by the 
action of phosphoric acid. 

233. Commercial Value of Phosphoric Acid. — The com- 
mercial value of phosphoric acid in fertilizers is deter- 
mined by the value of the crude phosphate rock, cost 
of grinding and treating with sulphuric acid, and cost of 



206 SOILS AND FERTILIZERS 

transportation. The price of phosphoric acid in super- 
phosphates usually ranges from 5 to 6 cents per pound. 
The field value, that is the increased yields obtained 
from the use of superphosphates, may .or may not be in 
accord with the commercial value because so many con- 
ditions influence crop growth. The phosphoric acid ob- 
tained from feed stuffs is usually considered worth about 
a cent a pound less than that from superphosphates. 
Water-soluble phosphoric acid is generally rated a half 
cent per pound higher than citrate-soluble phosphoric 
acid. 

234. Phosphate Slag. — In the refining of iron ores by 
the Bessemer process, the phosphorus in the iron is re- 
moved as a basic slag. The lime, which is used as a 
flux, melts and combines with the phosphorus of the 
ore, forming phosphate of lime. The slag has a variable 
composition. The process by which the phosphorus of 
pig iron is removed and converted into basic phosphate 
slag is known as the Thomas process, and the product 
is sometimes called Thomas' slag. At the present time 
but little basic slag is produced in this country that is 
suitable for fertilizer purposes. In Germany and some 
other European countries large amounts are produced 
and used. Phosphate slag is ground to a fine powder 
and is applied directly to the land, without undergoing 
the sulphuric acid treatment. The phosphoric acid is 
present mainly in the form of tetracalcium phosphate 
(CaO)^?^©^. 



PHOSPHATE FERTILIZERS 20/ 

235. Guano is the Spanish for dung and is a concen- 
trated form of nitrogenous and phosphate manure, of in- 
terest mainly on account of its historic significance. It 
is a mixture of sea-fowl droppings, with dead animals and 
debris, which have accumulated along the seacoast in 
sheltered regions and undergone fermentation. The 
introduction of guano into Europe marked an important 
period in agriculture, inasmuch as its use demonstrated 
the action and value of concentrated fertilizers. All of 
the best beds of guano have been exhausted and only a 
little of the poorer grades is now found on the market. 
The best qualities of guano contained from 12 to 15 per 
cent of phosphoric acid, 10 to 12 per cent of nitrogen, 
and from 5 to 7 per cent of alkaline salts. 

BONE FERTILIZERS 

236. Raw Bones contain, in addition to phosphate of 
lime, Ca3(P04)2, organic matter which makes them slow 
in decomposing and slow in their action as a fertilizer. 
Before being used as a fertiUzer they should be fer- 
mented in a compost heap with wood ashes in the follow- 
ing way, a protected place being selected so that no losses 
from drainage will occur. A layer of well-compacted 
manure is covered with wood ashes, the bones are then 
added and well covered with ashes and manure. From 
three to six months should be allowed for the bones to 
ferment. The large, coarse pieces may then be crushed 
and are ready for use. The presence of fatty material 



208 SOILS AND FERTILIZERS 

in a fertilizer retards its action because fat is so slow- 
in decomposing. Bones from which the organic matter 
has been removed are more active as a fertiHzer than raw 
bones. There is from i8 to 25 per cent of phosphoric 
acid and from 2 to 4 per cent of nitrogen in bones. 
The amount and value of the citrate-soluble phosphoric 
acid are extremely variable. 

237. Bone Ash is the product obtained when bones 
are burned. It is not extensively used as a fertilizer 
because of the greater commercial value of bone black. 
Bone ash contains about 36 per cent of phosphoric acid, 
and is more concentrated than raw bones. 

238. Steamed Bone. — Raw bones are subjected to 
superheated steam to remove the fat and ossein which 
are used for making soap and glue. They are then pul- 
verized and sold as fertiHzer under the name of bone meal, 
which contains from 1.5 to 2.5 per cent of nitrogen and 
from 22 to 29 per cent of phosphoric acid. Steamed 
bone makes a more active fertilizer than raw bone. Oc- 
casionally well-prepared bone meal is used for feeding 
pigs and fattening stock in the same way that flesh meal 
is used. The fineness to which the bone meal is ground 
greatly influences its agricultural value. 

239. Dissolved Bone. — When bones are treated with 
sulphuric acid, as in the manufacture of superphosphates, 
the product is called dissolved bone. The tricalcium 



PHOSPHATE FERTILIZERS 2O9 

phosphate undergoes a change to more available forms, 
as described, and the nitrogen is rendered more available. 
Dissolved bone contains from 2 to 3 per cent of nitrogen 
and from 15 to 17 per cent of phosphoric acid. 

240. Bone Black. — When bones are distilled, bone 
black is obtained. It is extensively employed for refin- 
ing sugar, and after it has been used and lost its power 
of decolorizing solutions it is occasionally sold for fertili- 
zer. It is a concentrated phosphate fertilizer, containing 
about 30 per cent phosphoric acid. 

241. Use of Phosphate Fertilizers. — The amount of 
a phosphoric acid fertilizer that it is advisable to apply 
to crops varies with the nature of the soil and the kind 
of crop to be produced. On a poor soil 400 pounds of 
acid phosphate per acre is an average application. It is 
usually appHed as a top dressing just before seeding, and 
may be placed near but not in contact with the seed. It 
is not advisable to make heavy applications of superphos- 
phates at long intervals, because fixation may take place 
to such an extent that crops are unable to utilize the 
fertilizer. Lighter and more frequent applications, as 
100 to 200 pounds per acre, are preferable. Phosphates 
should not be mixed with lime carbonate before spread- 
ing, but be appHed directly to the land.^^ Phosphates 
may be used in connection with farm manures. Many 
soils which contain Hberal amounts of phosphoric acid 
are improved by a light dressing of phosphates, 75 pounds 



210 



SOILS AND FERTILIZERS 



per acre. Such soils, however, should be more thor- 
oughly cultivated, and manured with farm manures, to 
make the phosphates available. There is frequently 
an apparent lack of phosphoric acid when in reality the 
trouble is due to other causes, as a deficiency of lime or 
organic matter to render the phosphates available. Be- 
fore using phosphate fertilizers, careful field tests should 
be made to determine the needs of the soil. 



242. How to keep the Phosphoric Acid Available. — 

Phosphoric acid associated with organic matter in a 
moderately alkaline soil is more available than that in acid 
soils. Soft phosphate rock may be mixed with manure or 
material like cottonseed meal and made slowly available 
for crops, but where land is high in price such a pro- 
cedure is not economical. Soils which contain a good 
stock of phosphoric acid, when kept well manured and 
occasionally limed if necessary, have a liberal supply 
of available phosphoric acid. The following is an 
example of two soils from adjoining farms, which 
have been cropped and manured differently.^^ 







Soil well 


No Manure and 






MANURED AND 


CONTINUOUS Wheat 






Ckops Rotated 


Raising 






Per Cent 


Per Cent 


Total phosphoric acid . . 




0.20 


0.20 


Humus 




4.25 


1.62 


Phosphoric acid dissolved 


with 




humus 




0.06 


0.02 



PHOSPHATE FERTILIZERS 211 

When the soil contains a liberal supply of total phos- 
phoric acid, it is more economical to change the phos- 
phoric acid of the soil to available forms by the use of 
farm manures, lime, rotation of crops, and thorough 
cultivation, than it is to purchase superphosphates in com- 
mercial forms. 



CHAPTER VIII 



POTASH FERTILIZERS 




Fig. 42. 



Oat Plant grown without Potash, 

212 



243. Potassium an Es- 
sential Element of Plant 
Food. — Potassium is one 
of the three elements 
most essential as plant 
food. In its absence 
plants are unable to de- 
velop. Oats seeded in 
a sterile soil from which 
potassium salts only were 
withheld made the total 
growth shown in the illus- 
tration ( Fig. 42). In dis- 
cussing the content of 
potassium compounds in 
plants, soils, and food 
stuffs, the term 'potash' 
(potassium oxide, K3O) 
is used. When present 
in the soil in liberal 
amounts and associated 
with other essential ele- 
ments, potash produces 



POTASH FERTILIZERS 



213 



vigorous plants. Like phosphoric acid and nitrogen, it 
is utilized by crops in the early stages of growth. It does 
not accumulate in seeds to the same extent as phosphoric 
acid and nitrogen, but is present mainly in stems and 
leaves ; consequently when straw crops are utilized in pro- 
ducing manure, the potash is not lost, or as in the case of 
nitrogen, sold from the farm. But with ordinary grain 
farming excessive losses of potash do occur, particularly 
when the straw is burned and the ashes are wasted. 

244. Amount of Potash removed in Crops. — In grain 
crops from 35 to 60 pounds of potash per acre are removed 
from the soil. For grass crops more potash is required 
than for grains, while roots and tubers require more than 
grass. The approximate amount of potash removed in 
various crops is given in the following table : 



Potash per Acre 
K,0 
Lbs. 



Wheat, 20 bu. 
Straw, 2000 lbs. 

Total 
Barley. 40 bu. 
Straw, 3000 lbs. 

Total 
Oats, 50 bu. 
Straw, 3000 lbs. 

Total 



35 

8 

30 

"38 
10 

35^ 
45 



214 



SOILS AND FERTILIZERS 



Corn, 65 bu. . . . 
Stalks, 3000 lbs. . 

Total . . 
Peas, 30 bu. 

Straw, 3500 lbs. . . 

Total . . . 

Flax, 15 bu. . . . 

Straw, 1800 lbs. . . 

Total . . 

Mangels, 10 tons . . 

Meadow liay, i ton . 
Clover hay, 2 tons 
Potatoes, 1 50 bushels 



Potash per Acre 
Lbs. 



15 

4^ 

60 
22 
38 
60 
8 

27 

150 

45 
66 

75 



245. Amount of Potash in Soils. — Ordinarily there 
is in soils from o. i to 0.5 per cent of potash, equivalent to 
from 3500 to 18,000 pounds per acre to the depth of 
one foot. Many soils with apparently a good stock of 
total potash give excellent results when a light dressing 
of potash salts is applied. The amount of available 
potash in a soil is more difficult to estimate than the 
available phosphoric acid. There is much difference in 
crops as to their power of obtaining potash ; some re- 
quire greater help in procuring it than others. A lack 



POTASH FERTILIZERS 21$ 

of available potash is sometimes indirectly due to a 
deficiency of lime or other alkaline matter in the soil, 
which prevents the necessary chemical changes taking 
place in order that the potash may be liberated as plant 
food. 

246. Sources of Potash in Soils. — The main source 
of the soil's potash is feldspar, which, after disintegra- 
tion, is broken up into kaolin and potash compounds. 
Mica and granite also, in some localities, contribute lib- 
eral amounts, and the zeolitic silicates are a valuable 
source of potash. There is but little water-soluble pot- 
ash except in alkaline soil. By the action of many fer- 
tilizers the potash compounds undergo changes in com- 
position. For example, the gypsum which is always 
present in acid phosphates liberates some potash. The 
potash compounds of the soil are in various degrees of 
complexity from forms soluble in dilute acids to insoluble 
minerals as feldspar. 

247. Commercial Forms of Potash. — Prior to the in- 
troduction of the Stassf urt salts, wood ashes were the main 
source of potash. Since the discovery and development 
of the Stassfurt mines, the natural products, as kainit, 
and muriate and sulphate of potash, have been exten- 
sively used for fertilizing purposes. A small amount of 
potash is obtained also from waste products, as tobacco 
stems, cottonseed hulls, and the refuse from beet-sugar 
factories. 



2l6 SOILS AND FERTILIZERS 



STASSFURT SALTS 



248. Occurrence.^* — The Stassfurt mines were first 
worked with the view of procuring rock salt. The va- 
rious compounds of potash, soda, and magnesia, asso- 
ciated with the layers of rock salt, were regarded as 
troublesome impurities, and attempts were made by 
sinking new shafts to avoid them, but with the resu!t 
of finding them in greater abundance. About 1864 
their value as potash fertilizer was established. It is 
supposed that at one time the region about the mines 
was submerged and filled with sea water. The tropi- 
cal climate of that geological period caused rapid evapo- 
ration, which resulted in forming mineral deposits, the 
less soluble material as lime sulphate being first depos- 
ited, then a layer of rock salt, and finally layers of pot- 
ash and magnesium salts in the order of their solubility. 

249. Kainit is a niineral composed of potassium 
sulphate, magnesium sulphate, magnesium chloride, and 
water of crystallization. As it comes from the mine 
it is mixed with gypsum, salt, potassium chloride, and 
other bodies. Kainit contains about 12 per cent potash 
and is one of the most important of the Stassfurt salts. 
It is extensively used as a potash fertilizer, and is also 
mixed with other materials and sold as a complete fer- 
tilizer. The magnesium chloride causes it to absorb 
water, and the presence of other compounds results 
in the formation of hard lumps, whenever kainit is 



POTASH FERTILIZERS 217 

kept for a long time. Kainit is soluble in water 
and can be used as a top dressing at the rate of 75 
to 200 pounds or more per acre. 

250. Muriate of Potash. — This is extensively used as 
a fertilizer and is valuable for general garden and farm 
crops. It is a manufactured product, — potassium chlo- 
ride, — and ranges in purity from 60 to 95 per cent, 
equivalent to from 35 to 60 per cent of potash, the 
chief impurity being sodium chloride. The grade most 
commonly found on the market contains about 50 
per cent of actual potash, equivalent to 80 per cent 
of muriate. Potassium chloride is readily soluble and 
is a quick-acting fertilizer. When used in large 
amounts, muriate of potash and other chlorides may un- 
favorably affect the quality of some crops, as potatoes, 
sugar beets, and tobacco. Ordinarily, muriate of pot- 
ash is one of the cheapest and most active forms of 
potash, and can be used as a top dressing at the rate 
of 200 pounds or more per acre when preparing 
soils for crops. It is valuable for grass and grain 
crops, and has given good results on peaty lands.^^ 

251. Sulphate of Potash. — High-grade sulphate of 
potash is prepared from some of the crude Stassfurt 
salts and may contain as high as 97 per cent K2SO4, 
equivalent to 50 per cent of potassium oxide (KgO). It 
is one of the most concentrated forms of potash fer- 
tilizer and is particularly valuable because it can be 



2l8 



SOILS AND FERTILIZERS 



applied safely to crops, as tobacco and potatoes, which 
would be injured in quality if muriate of potash were 
used, or if much chlorine were present. Low-grade 
sulphate of potash is 90 per cent pure. 

252. Miscellaneous Potash Salts. — Carnallit, 9 per 
cent K^O, — composed of KCl,MgCl2,6 H2O. Polyha- 
lit, 15 per cent K2O, — composed of K3S04,MgS04. 
(CaS04)2,H20. Krugit, 10 per cent K2O, — composed 
of K2Sd'4,MgS04,(CaS04)4,H30. Sylvinit, 16 to 20 per 
cent KgO, — composed of KCl,NaCl and impurities. 
Kieserit, 7 per cent K2O, — composed of MgS04 and 
carnallit. 

253. Wood Ashes. — For ordinary agricultural pur- 
poses, wood ashes are an important source of potash, 
although they are exceedingly variable in composition. 
When leached the soluble salts are extracted and there 
is left only about i per cent of potash. In unleached 
ashes the amount of potash ranges from 2 to 10 per 
cent. Soft wood ashes contain much less potash than 
hard wood ashes. Goessmann gives the following as 
the average of 97 samples of ashes : ^^ 



Average 

Composition 

Per Cent 



Range 
Per Cent 



Potash . . . 
Phosphoric acid 
Lime 



5-5 
1.9 

34-3 



2,5 to 10.2 
0.3 to 4.0 
180 to 50.9 



potash fertilizers 
In 10,000 Pounds of Wood 



219 



Phosphoric 
Acid 
Lbs. 



White oak 
Red oak . 
Ash . . 
Pine . . 
Georgia pine 
Dogwood . 




254. Action of Ashes on Soils. — Ashes act upon soils 
both chemically and physically. They are usually re- 
garded as a potash fertilizer only, but they also contain 
lime and phosphoric acid, and may be very beneficial 
in supplying these elements. The potash is present 
mainly as potassium carbonate. Ashes are valuable, 
too, because they add alkaline matter to the soil, which 
corrects acidity and aids nitrification. A dressing of 
ashes improves the mechanical condition of many soils 
by binding together the soil particles. This property 
is well illustrated in the so-called Gumbo soils, which 
contain so much alkaline matter that the soil has a soapy 
taste and appearance, and when plowed the particles fail 
to separate. 

255. Leached Ashes. — When ashes are leached the 
soluble salts are extracted; the insoluble matter which 
is left is composed mainly of calcium carbonate and 
silica.*^*^ 



220 



SOILS AND FERTILIZERS 



Water 

Silica, etc. . . . 
Potassium carbonate 
Calcium carbonate . 
Phosphoric acid . . 



Unleached Ashes 


Leached Ashes 


Per Cent 


Per Cent 


I2.0 


30.0 


13.0 


13.0 


5-5 


I.I 


61.0 


51.0 


1.9 


1.4 



256. Alkalinity of Leached and Unleached Ashes. — 

A good way to detect leached ashes is to determine the 
alkalinity in the following way : weigh out 2 grams of 
ashes into a beaker, add 100 cc. distilled water, and 
heat on a sand bath nearly to boiling, cool and filter. 
To 50 cc. of the filtrate add about 3 drops of cochineal 
indicator, and then a standard solution of hydrochloric 
acid from a burette until the solution is neutral. If a 
standard solution of acid cannot be procured, one con- 
taining 15 cc. concentrated hydrochloric acid per liter 
of distilled water may be used for comparative pur- 
poses. Leached ashes require less than 2 cc. of acid 
to neutrahze the alkaline matter in i gram, while un- 
leached ashes require from 10 to 18 cc. In purchasing 
wood ashes, if a chemical analysis cannot be secured, 
the alkalinity of the ash should be determined. 



257. Coal and Other Ashes. — Since the amount of 
phosphoric acid and potash in coal ashes is very small, 
they have httle fertilizer value. Soft coal ashes contain 



POTASH FERTILIZERS 



221 



more potash than those from hard coal, but it is held in 
such firm combination as to be of but little value. 

The ashes from sawmills where soft wood is burned, 
and they are unprotected, are nearly worthless. When 
peat bogs are burned over, large amounts of ashes are 
produced. If the bogs were covered with timber, the 
ashes are sometimes of sufficient value to warrant their 
transportation and use. 



Hard coal ashes .... 
Soft coal ashes . . . . , 
Sawmill ashes ^* . . . . , 
Peat bog ashes ^'^ . . . . 
Peat bog ashes (timbered) ^^ 
Tobacco stem ash ... 
Cottonseed hulls, ash . . 



Phosphoric 

Acid 
Per Cent 




258. Commercial Value of Potash. — The market value 
of potash is governed by the selling price of high-grade 
sulphate of potash and kainit. Ordinarily, it varies 
from 4 to 5 cents per pound. As in the case of nitro- 
gen and phosphoric acid, the market and field values, 
as determined by crop yields, may be entirely at vari- 
ance. Before potash salts are used, careful field tests 
should be made to determine the actual condition of the 
soil as to its need of potash. (See Chapter X, Commer- 
cial Fertilizers.) 



222 SOILS AND FERTILIZERS 

259. Use of Potash Fertilizers. — Wood ashes or 
Stassfurt salts should not be used in excessive amounts. 
Not more than 300 pounds per acre should be applied 
unless the soil is known to be markedly deficient in 
potash, and previous tests indicate that larger amounts 
are safe and advisable. Potash fertilizers should be 
evenly spread and not allowed to come in direct con- 
tact with plant roots, and should be used early in the 
spring before seeding or before the crop has made 
much growth. Wood ashes make an excellent top 
dressing for grass lands, particularly where it is de- 
sired to encourage the growth of clover. There are 
but few crops or soils that are not greatly benefited 
by a light application of wood ashes, and none should 
ever be allowed to leach or waste about a farm. 

260. Joint Use of Lime and Potash. — When a potash 
fertilizer is used, a dressing of lime will frequently be 
found beneficial. The potash undergoes fixation, and 
when it is liberated there should be some basic material 
as lime to take its place. Goessmann observed that 
land manured for several years with potassium chlo- 
ride finally produced sickly crops, but an application 
of slaked lime restored a healthy appearance to suc- 
ceeding crops.^'' If the soil is well stocked with lime, 
its joint use with potash fertilizers is not necessary. 
If it is acid, lime should be used to correct the acidity 
before the potash is applied. The use of potash fer- 
tilizers for special crops is discussed in Chapter X. 



CHAPTER IX 
LIME AND MISCELLANEOUS FERTILIZERS 



261. Calcium an Essential 
Element of Plant Food. — Cal- 
cium is present in the ash of 
all plants, and is usually more 
abundant in soils than phos- 
phorus or potassium. It takes 
an essential part in plant 
growth, and whenever with- 
held growth is checked. The 
effect of withholding calcium 
is shown in the illustration 
(Fig. 43), which gives the 
total growth made by an oat 
plant under such a condition. 

Plants grown on soils defi- 
cient in calcium compounds 
lack hardiness. They are not 
so able to withstand drought 
or unfavorable climatic condi- 
tions as plants grown on soils 
well supplied with this element. 
Calcium does not accumulate 
in the seeds of plants, but is 
present mainly in the leaves 




Fig. 43. 



Oat Plant grown with- 
out Calcium. 



224 



SOILS AND FERTILIZERS 



and stems, where it takes an important part in the pro- 
duction of new tissue. The term ' lime/ when used in 
connection with crops and soils, refers to their content 
of calcium oxid, CaO. 



262. Amount of Lime removed in Crops. 



38 



Pounds per Acre 
CaO 



Wheat, 2o bushels 
Straw, 2000 pounds 

Total 
Corn, 65 bushels . 
Stalks, 3000 pounds 

Total 
Peas, 30 bushels . 
Straw, 3500 pounds 

Total 
Flax, 15 bushels . 
Straw, 1800 pounds 

Total 
Clover, 4000 pounds 



I 

_7 
8 

I 

II 
12 

4 

ZL 

75 
3 

_y 
16 

75 



Clover and peas remove so much lime from the soil 
that they are often called lime plants. The amount 
required by grain and hay is small compared with that 
required by a clover or pea crop. 



263. Amount of Lime in Soils. — There is no other 
element in the soil in such variable amounts as cal- 
cium, popularly called lime. It may be present from 



LIME AND MISCELLANEOUS FERTILIZERS 22 5 

one hundredth of a per cent to 20 per cent or 
more. Soils which contain from 0.3 to 0.5 per cent, 
as carbonate, are usually well supphed. The lime in 
a soil takes an important part in soil fertility ; when 
it is wanting, humic acid may be formed, nitrification 
checked, and the soil particles will lack binding mate- 
rial. Calcium carbonate is somewhat soluble in soil 
water, due to the presence of carbon dioxide. Waters 
are hard because of the presence of lime. The loss of 
lime by leaching has caused many soils to become 
unproductive. 

264. Different Kinds of Lime Fertilizers. — By the 

term * lime fertilizer ' is usually meant land plaster 
(CaS04, 2 H2O). Occasionally quicklime (CaO) and 
slaked Hme (Ca[OH]2) are used on very sour land. In 
general, a lime fertilizer is one which supplies the ele- 
ment calcium ; common usage, however, has restricted 
the term to sulphate of lime. 

j 

i 265. Action of Lime Fertilizers upon Soils. — Lime 

1 fertilizers act both chemically and physically. Chemi- 

j cally, Hme unites with the organic matter to form 

humate of lime and thus prevents the formation of 
I humic acid. It also aids in nitrification and acts upon 
j the soil, liberating potassium and other elements of plant 

food. Physically, lime improves capillarity, precipitates 
I clay when suspended in water, and prevents losses, as 
! the washing away of fine earth. When soils are defi- 
Q 



226 



SOILS AND FERTILIZERS 



cient in lime, an acid condition may develop to such 
an extent as to be injurious to vegetation. Nitrogen, 
phosphoric acid, and potash may all be present in liberal 
amounts, but in the absence of lime poor results are 
obtained. Because of the loss by drainage, removal 
as plant food and the chemical reaction in which it 
takes a part, there is greater necessity for a liberal 
supply of active lime compounds in a soil than of any 
other element of plant food. 

266. Lime liberates Potash. — The action of lime 
upon soils well stocked with potash results in fixation 
of the lime and liberation of the potash ; the reaction 
takes place in accord with the well-known exchange of 
bases explained in the chapter on fixation. The extent 
to which potash may be liberated by lime depends upon 
the firmness of chemical combination with which the 
potash is held in the soil. Boussingault found that 
when clover was limed there was present in the crop 
three times as much potash as in a similar crop not 
limed. His results are as follows :^^ 



Lime . . . . 
Potash . . . , 
Phosphoric acid 



Kilos per Hectare 



In Crop not Ltmed 



First 

year 

32.2 
26.7 
II.O 



Second 
year 

•52.2 

28.6 

7.0 



In Limed Crop 



First 
year 

794 
95.6 
24.2 



Second 
year 

102.8 
97.2 
22.9 



LIME AND MISCELLANEOUS FERTILIZERS 22/ 

The indirect action of land plaster upon western 
prairie soils in liberating plant food, particularly potash 
and phosphoric acid, is unusually marked. Laboratory 
experiments show that small amounts of gypsum are 
quite active in rendering potash, phosphoric acid, and 
even nitrogen soluble in the soil water. '^ Occasionally 
applications of superphosphate fertilizers give large 
yields, due to the gypsum which they contain, and not 
to the phosphorus. 

267. Quicklime and Slaked Lime. — When it is de- 
j sired to correct acidity, slaked lime is used. Air-slaked 
I lime is not so valuable as water-slaked lime. Quick- 
' lime cannot be used on land after a crop has been 
1 seeded. Both slaked lime and quicklime should be 
i applied some little time before seeding, and not to the 
\ crop. The action of quicklime upon organic matter 
' is so rapid that it destroys vegetation. Slaked lime is 
■ less injurious to vegetation. 

I 268. Pulverized Lime Rock. — In some localities pul- 
] verized hme rock is used. It may be applied as a top 
I dressing in almost unlimited amounts. It is most 
J beneficial on light, sandy soils, where it performs the 
I function of fine clay as well as promoting chemical 
: action. Acid soils also are benefited by its use. Not 
I all soils are alike responsive to applications of lime- 
I stone, and before using it is best to determine to what 
I extent it is needed. There are no ordinary conditions 



228 SOILS AND FERTILIZERS 

where limestone is injurious to soil or crop, and it is 
frequently most helpful. 

269. Marl. — Underlying beds of peat, deposits of 
marl are occasionally found. Marl is a mixture of 
disintegrated limestone and clay, and contains variable 
amounts of calcium carbonate, phosphoric acid, and 
potash. When peat and marl are found together, they 
may be used jointly with manure as described in Sec- 
tion 182. Many sandy lands in the vicinity of peat 
and marl deposits would be greatly improved, both 
physically and chemically, by these materials. 

270. Physical Action of Lime. — The addition of lime 
fertilizers to sandy soils improves their general physi- 
cal condition. Heavy clays lose their plasticity when 
limed and the fine clay particles are cemented together 
and act as sand, which improves the mechanical con- 
dition of the soil. The physical action of lime in soils 
is well illustrated in the case of ' loess soils,' which are 
composed of clay and limestone. The lime cements 
together the clay particles to form compound grains, 
making the soil more permeable and more easily tilled. 
The better physical 'condition which follows the appli- 
cation of lime fertilizers is frequently sufficient to war- 
rant their use. 

271. Application of Lime Fertilizers. — Lime is gener- 
ally used as a top dressing on grass lands at the rate of 
200 to 500 pounds per acre. Excessive applications are 



LIME AND MISCELLANEOUS FERTILIZERS 229 

undesirable. Lime as gypsum is particularly valuable 
when applied to land where crops are grown which 
assimilate large amounts, as clover and other legumes. 
It should be remembered that it is not a complete 
fertilizer, but simply an amendment and an indirect 
fertilizer.^ If used to excess it may get the soil in such 
condition that plant food is not easily rendered avail- 
able. A common saying is, " Lime makes the father 
rich but the son poor."^^ This is true, however, only 
when lime is used in excess. When used occasionally 
in connection with other manures, it has no injurious 
effect upon the soil and is a valuable fertilizer, especially 
where clover is grown with difficulty. 

MISCELLANEOUS FERTILIZERS 

272. Salt is frequently used as an indirect fertiHzer. 
Sodium and chlorine, the two elements of which it is 
composed, are not absolutely necessary for normal 
plant growth. When salt is applied to the soil and 
the sodium undergoes fixation, potassium may be lib- 
erated. An early experiment of Wolff illustrates this 
point : a buckwheat plot fertilized with salt produced 
a crop with more potash and less sodium than a similar 
unfertilized plot. 

Salt may be used to check the rank growth of straw 
during a rainy season, and thus prevent loss of the 
crop by lodging, although not in excessive amounts, as 
it is destructive to vegetation ; 200 pounds per acre is a 



230 SOILS AND FERTILIZERS 

fair application. Salt also improves the physical con- 
dition of the soil by increasing the surface tension of 
the soil water. It should not be used on a tobacco or 
potato crop, because it injures the quality of the product. 
Salt is beneficial in preventing some forms of fungous 
diseases from becoming established in soils. 

273. Magnesium Salts. — Magnesium is present in the 
ash of all plants, and is an element essential for plant 
growth. Usually soils are so well stocked with mag- 
nesium that it is not necessary to apply it in ferti- 
lizers. Some of the magnesium salts, as the chloride, 
are injurious to vegetation, but when associated with 
lime as carbonate, magnesia imparts fertility. In many 
of the Stassfurt salts, magnesium is found. 

274. Soot. — The deposits formed in boiler flues and 
chimneys when wood and soft coal are burned contain 
small amounts of potash and phosphoric acid. Soot is 
valuable mainly as a mechanical fertilizer and is slow 
in decomposing. It contains but little plant food as 
shown by the following analysis : 



Potash . . . 
Phosphoric acid 



Soft Coal Soot 
Per Cent" 



0.84 
0.75 



Hard Wood Soot 
Per Cent™ 



1.78 
0.96 



275. Seaweeds. — Seaweeds are rich in potash and 
near the seacoast are extensively used for fertilizer. 



LIME AND MISCELLANEOUS FERTILIZERS 23 1 



Composition of 

Mixed Seaweeds 

Per Cent™ 



Water . . . . 
Nitrogen . . . 
Potash . . . . 
Phosphoric acid 



81.50 

0.73 
1.50 
0.18 



Weeds and plants produced on waste land along the 
sea are in some European countries burned and the 
ashes used as fertilizer. By this means waste land is 
made to produce fertilizer for fields which are tillable. 

276. Weeds. — The amount of fertility removed in 
weeds is usually more than in agricultural plants, be- 
cause weeds have greater power of obtaining food from 
the soil. When wheat or other grain is raised, and a 
small crop of grain and a large crop of weeds are the 
result, there is more fertility removed from the soil than 
if a heavy stand of grain had been obtained. The ashes 
of strand plants and weeds are extremely variable in 
composition. 

277. "Wool Washings and Waste. — The washings from 
wool contain sufficient potash to make them valuable as 
fertilizer. In wool there is a high per cent of potash, 
which is soluble and readily removed in the washings. 
Wool waste may contain from i to 5 per cent of potash 
and from 4 to 7 per cent of nitrogen in a somewhat 
inert form. 



232 SOILS AND FERTILIZERS 

278. Street Sweepings. — The horse manure and de- 
bris collected from paved streets in cities and known 
as street sweepings have some value as fertilizer, and 
are occasionally used for market gardening purposes. 
Street sweepings, because of the loss of the liquid 
excrements, have a lower value than average stable 
manure and cannot be used economically when labor 
and the cost of hauling are high-priced, or when a 
quick-acting manure is desired. For sanitary reasons, 
the use of street sweepings is not always desirable, as 
mixed with the horse droppings frequently are associ- 
ated accumulations of filth from dwellings contaminated 
with disease germs. Crude garbage has a low manurial 
value ; when sorted and cremated, the burned residue 
can be used to better advantage as fertilizer than the 
raw garbage, and is without the objectionable and un- 
sanitary features. 



CHAPTER X 
COMMERCIAL FERTILIZERS AND THEIR USE 

279. Development of the Commercial Fertilizer Indus- 
try. — The commercial fertilizer industry owes its origin 
to Leibig's work on plant ash. The first superphos- 
phate was made by Sir J. B. Lawes about 1840, from 
spent bone black and sulphuric acid. His interest had 
previously been attracted to the use of bones as fer- 
tilizer by a gentleman who farmed near him, " who 
pointed out that on one farm bone was invaluable for 
the turnip crop, and on another farm it was useless."** 

Since i860 the commercial fertilizer industry in this 
country has developed rapidly, until now large sums of 
money are annually expended in purchasing commercial 
fertilizers and amendments, and nearly all in less than 
a third of the area of the United States. 

280. Complete Fertilizers and Amendments. — The 

term ' commercial fertihzer ' is applied to materials made 
by mixing different substances which contain plant 
food in concentrated forms. When a commercial fer- 
tilizer contains nitrogen, phosphoric acid, and potash, 
it is called a complete fertilizer, because it supplies the 
three elements which are liable to be most deficient. 

233 



234 SOILS AND FERTILIZERS 

Materials as sodium nitrate which supply only one ele- 
ment are called amendments. It frequently happens 
that a soil requires only one element in order to produce 
good crops, and in such cases only the one element 
needed should be supplied. 

Complete fertilizers are often used when the soil is 
in need of an amendment only. 

281. Variable Composition of Commercial Fertilizers. 
— Since commercial fertilizers are made by mixing 
various materials which contain different amounts of 
nitrogen, phosphoric acid, and potash, it follows they 
are extremely variable in composition and value. No 
two samples are the same, hence the importance of 
knowing the composition of every brand purchased. 
The composition of fertilizers is varied to meet the 
requirements of different soils and crops. Some ferti- 
lizers are made rich in phosphoric acid, while others are 
rich in nitrogen and potash. 

282. How a Fertilizer is Made. — The most common 
materials used in making complete fertilizers are : ni- 
trate of soda, kainit, and dissolved phosphate rock. 
These materials have about the following composition : 

Nitrate of soda 15.5 per cent nitrogen. 

Kainit 12.5 per cent potash. 

Dissolved phosphate . . . 14.0 per cent phosphoric acid 

The fertilizer may be made rich or poor in any ingre- 
dient. Many fertilizers contain about twice as much 



COMMERCIAL FERTILIZERS AND THEIR USE 235 

potash as nitrogen and five times as much phosphoric 
acid as potash. In order to make a ton of such a ferti- 
Hzer it would be necessary to take : 



Pounds 



Nitrate of soda 
Kainit . . . 
Phosphate . . 



225 

425 

1350 



The ton of fertihzer would contain about 35 pounds 
of nitrogen, 189 pounds of phosphoric acid, and 53 
pounds potash. These amounts are determined by 
multiplying the percentage composition by the weight 
of material taken : 

Pounds 

Nitrogen 225 x 0.155 = 34.9 

Potash 425 X 0.125 = 53-' 

Phosphoric acid 1350 x 0.14 = 189.0 

The fertilizer would contain about 1.75 per cent ni- 
trogen, 2.65 per cent potash, and 9.45 per cent phos- 
phoric acid. The percentage amounts are obtained by 
dividing the total pounds by 20. This fertilizer if made 
at home from materials purchased in the market, at the 
prices indicated, would cost, exclusive of transportation 
and mixing, about $21.47. 

Pounds Cost 

Nitrogen 34.9 @ 16 cents = $5.58 

Phosphoric acid .... 189.0 @ 7 cents = 13.23 
Potash 53-1 @ 5 cents = 2.66 

Total $21.47 



236 SOILS AND FERTILIZERS 

A more concentrated fertilizer could be prepared by 
using high-grade sulphate of potash, superphosphate, 
and ammonium sulphate. A fertilizer composed of 
these ingredients would contain : 

b 

O 

O O K 

^ES 

WgS 
u ^ h 

Pounds Per Cent t„^ Value wow 

L,BS. PmU&h 

300 Sulphate of ammonia 20 N 60 @ 16 cents = $ 9.60 3.00 

500 Sulphate of potash . 50 KjO 250 @ 5 cents = 12.50 12.50 

1200 Superphosphate . . 35 P^O^ 420 @ 7 cents = 29.40 21.00 

Total $51.50 

So concentrated a fertilizer as the preceding is rarely, 
if ever, found on the market, although the price, ^51.50 
per ton, is frequently charged. This example shows 
the composition and cost of the ingredients in one 
of the most concentrated fertilizers that can be pro- 
duced. 

The market value of the materials of which commer- 
cial fertilizers are made fluctuates Hke that of other com- 
modities. 

Any of the different materials mentioned in the 
chapters on special fertilizers can be used in making 
commercial fertilizers, as dried blood, tankage, nitrate 
of soda, sulphate of ammonia, raw bone, dissolved 
bone, raw phosphate rock, dissolved phosphate rock, 
basic slag, kainit, muriate or sulphate of potash, and 
many others. Inasmuch as each of these materials 
has a different value, it follows that fertilizers, even 



COMMERCIAL FERTILIZERS AND THEIR USE 23/ 

of the same general composition, may have widely 
different crop-producing powers. 

283. Inert Forms of Plant Food in Fertilizers. — A 

fertilizer of the same general composition as the first 
example, but of different availability of the elements, 
could be made from feldspar rock, apatite rock, and 
leather. The leather contains nitrogen, the apatite 
contains phosphoric acid, and the feldspar, potash. 
Such a fertilizer would have no value when used on a 
crop, because all the plant food elements are present 
in unavailable forms. Hence, in purchasing fertilizers, 
it is necessary to know not only the percentage com- 
position, but also the nature of the materials from which 
the fertilizer was made. Inert forms of plant food are 
akin to indigestible forms of animal food ; it is the food 
which is assimilated that is of value whether it be by 
animals or by plants. 

284. Inspection of Fertilizers. — In many states, laws 
have been enacted regulating the manufacture and sale 
of commercial fertilizers, and provision is made for 
inspection and analysis of all brands offered for sale. 
The label on the fertilizer package must specify the 
percentage amounts of available nitrogen, phosphoric 
acid, and potash. Inspection has been found necessary 
in order to protect the farmer and the honest manu- 
facturer. As the result of inspection and analysis, 
occasionally a fraud is revealed like the following : ''^ 



238 SOILS AND FERTILIZERS 

Natural Plant Food, $25 to $28 per Ton 

Composition 



Total phosphoric acid 

Insoluble phosphoric acid 

Available phosphoric acid . . . . 

Potash soluble in water 

Actual value per ton, $1.52 




285. Mechanical Condition of Fertilizers. — In pur- 
chasing a fertilizer its mechanical condition should be 
considered. The finer the fertiUzer, as a rule, the bet- 
ter it is for promoting crop growth. Some combina- 
tions of plant food produce fertilizers which become so 
hard and lumpy that it is difficult to crush them before 
spreading. They should be pulverized so they may be 
evenly distributed, otherwise the plant food will not be 
economically used. A fertilizer that passes through a 
sieve with holes 0.25 mm. in diameter is more valuable 
and can be used to better advantage than one of the 
same composition with particles 0.5 mm. in size. 

286. Forms of Nitrogen in Commercial Fertilizers. — 

Nitrogen is present in commercial fertilizers in three 
forms : (i) Ammonium salts, (2) nitrates, and (3) 
organic nitrogen. The organic nitrogen is divided 
into two classes: (a) available, and (d) unavailable. 
Pepsin and also potassium permanganate are used as 
solvents for determining the availability of the organic 



COMMERCIAL FERTILIZERS AND THEIR USE 



239 



nitrogen. The relative values of the different forms 
of nitrogen are discussed in Chapter IV. Three fer- 
tilizers may have the same amount of total nitrogen 
and still have entirely different crop-producing powers. 



Nitrogen as : 

Ammonium compounds 
Nitrates ...... 

Organic nitrogen : 

Soluble ■ 

Insoluble 

Total . . . 



No. I 
Per Cent 



0.15 



No. 2 
Per Cent 



0.25 
0.15 

1.25 
0-35 



No. 3 
Per Cent 



O.IO 
O.IO 

0.55 
1.25 



In purchasing fertilizers it is important to know not 
only the amount of nitrogen, but also the form in 
which it is present. In No. 3 the nitrogen is in an 
inert form as in leather, while in No. 2 it is largely in 
the form of dried blood, and No. i has mainly am- 
monium compounds. Each of these fertilizers, as ex- 
plained in the chapter on nitrogenous manures, has a 
different plant food value. 



287. Phosphoric Acid. — There are three forms of 
phosphoric acid "in commercial fertilizers: (i) water 
soluble, (2) citrate-soluble, and (3) insoluble. The 
water and citrate-soluble are called the available phos- 
phoric acid. In most fertilizers the phosphoric acid is 
derived from dissolved phosphate rock and is in the 



240 



SOILS AND FERTILIZERS 



form of monocalcium phosphate. The citrate-soluble 
is mainly dicalcium phosphate with variable amounts 
of iron and aluminum phosphates in easily soluble 
forms. The insoluble phosphoric acid is tricalcium 
and other phosphates, as iron and aluminum, which 
are soluble only in strong mineral acids. The insoluble 
phosphoric acid in fertilizers is considered as having 
but little value. As in the case of nitrogen, three 
fertihzers may have the same total amount of phos- 
phoric acid and yet have entirely different values. 







No. I 
Per Cent 


No. 2 
Per Cent 


No. 3 
Per Cent 


Water-soluble phosphoric acid . . . 
Citrate-soluble phosphoric acid . . . 
Insoluble 


8.00 
1.50 
0.50 


0.25 

8.00 
175 


0.25 

0.75 

9.00 




Total 


10.00 


10.00 


10.00 







No. 3 has little value ; it contains insoluble phos- 
phate rock or some material of the same nature. No. i 
is the most valuable, because it contains dissolved 
phosphate rock or dissolved bone and but little insoluble 
phosphoric acid. No. 2 is composed of such materials 
as the best grade of basic slag or roasted aluminum 
phosphate or fine steamed bone. 



288. Potash. — The three forms of potash in fertili- 
zers are: (i) water-soluble, (2) acid-soluble, and (3) in- 
soluble. Sulphate of potash, kainit, and muriate of 



COMMERCIAL FERTILIZERS AND THEIR USE 241 

potash are soluble in water and belong to the first class. 
In some states the fertilizer laws recognize only the 
water-soluble potash. In the second class are found 
materials like tobacco stems and other organic forms of 
potash. Substances like feldspar, which contain insol- 
uble potash, are of no value in fertilizers. As a rule, 
the potash in commercial fertilizers is soluble in water ; 
in only a few cases are acid-soluble forms met with. 
Insoluble potash is considered an adulterant. 

289. Misleading Statements on Fertilizer Packages. — 

Occasionally the percentage amounts of nitrogen, phos- 
phoric acid, and potash are stated in misleading ways : 
as ammonia, sulphate of potash, and bone phosphate of 
lime. Inasmuch as ammonia contains 14 parts nitro- 
gen and 3 parts by weight of hydrogen, it follows the 
ammonia content is proportionally greater than the 
nitrogen content, because of the additional hydrogen 
carried by the ammonia. And so with sulphate of 
potash, which contains about 50 per cent potash and 50 
per cent of sulphuric anhydride. This method of stat- 
ing the composition can be considered in no other way 
than as a fraud, especially when the fertilizer contains 
no sulphate of potash, but cheaper materials, and the 
phosphoric acid is not derived from bone. 

290. Estimated Commercial Value of Fertilizers. — 

The estimated value of a commercial fertilizer is ob- 
tained from the percentage composition and the trade 



242 SOILS AND FERTILIZERS 

value of the materials used. Suppose two fertilizers 
are selling at $28 and $35, respectively, each having a 
different composition, the estimated value of each could 
be obtained in the following way : 

Composition of Fertilizers 

No. I No. 2 

Selling Price $28 Selling Price $35 

Per Cent Per Cent 

Nitrogen as nitrates 1.50 2.10 

Phosphoric acid, available . . .8.00 10.00 

Phosphoric acid, insoluble . . . 2.00 0.50 

Potash (water-soluble) .... 2.00 3.50 

Pounds per Ton 

No. I No. 2 

Nitrogen . . . 1.50 x 20 = 30 2.10 x 20 = 42 

Phosphoric acid . 8.00 x 20 = 160 10.00 x 20 = 200 
Potash .... 2.00 x 20 = 40 3.50 X 20 = 70 

Estimated Value 

No. I 
Nitrogen . . . . 30 x 0.16 = $ 4.80 
Phosphoric acid . . 160 x 0.07 = 11.20 
Potash 40 X 0.05 = 2.00 

$18.00 
Difference between estimated value and selling price 
$10.00 ; No. 2, $10.78. 

The trade value of a commercial fertilizer often varies 
widely from the actual or crop-producing value, for in j 
assigning a trade value simply the cost of the ingredi- 1 
ents is considered, and this is not necessarily identical 





No. 2 


42 X 0.16 


= $ 6.72 


:oo X 0.07 


= 14.00 


70 X 0.05 


= 3-5° 




$24.22 


ing price : 


No. I, 



COMMERCIAL FERTILIZERS AND THEIR USE 



243 



with the actual value secured in increased yield from 
the use of the fertilizer. 



291. Home Mixing of Fertilizers. — At the New 
Jersey Experiment Station it was shown that "the 
charges of the manufacturers and dealers for mixing, 
bagging, shipping, and other expenses are on the aver- 
age $8.50 per ton, and also that the average manu- 




FlG. 44. Composition of Fertilizers. 

factured fertiUzer contains about 300 pounds of actual 
fertilizing constituents per ton. These figures are prac- 
tically true of other states, where large quantities of 
commercial fertilizers are used."'^^ In states where 
smaller amounts are used the difference between the 
estimated cost and selling price is greater than $8.50. 

These facts emphasize the economy of home mixing. 
The difference in price between the raw materials and 
the product sold is frequently so great that it is an ad- 
vantage for the farmer to purchase the raw materials, 
as sulphate of potash, nitrate of soda, and acid phos- 



244 



SOILS AND FERTILIZERS 



phate, and mix them as desired. By so doing fertilizers 
of any composition may be prepared and there is less dan- 
ger of securing an inferior article. Of course it is not 
possible by means of shovels and sieves to accomplish as 
thorough mixing of the ingredients as with machinery. 



Nitrate of soda . 
Acid phosphate . 
Sulphate of potash 



Formula No. i 

Pounds 

500 containing nitrogen . 

. 1200 containing phos. acid . 

, 300 containing potash . . 



Total 



Nitrate of soda 
Acid phosphate . 
Sulphate of potash 
Plaster, etc. . . 

Total . . 



Formula No. 3 
200 containing nitrogen 
1500 containing phos. acid 
1 50 containing potash . 
150 



Pounds 

77-5 
168.0 



150.0 7.50 



3897 



316.0 



w z 

o o « 
2h« 



b: S es 
u o H 

3-87 
8.40 



Total . . . 


Formula No. 2 


• 395-5 




Nitrate of soda . , 


, 250 containing nitrogen . 


• 38.7 


1-99 


Acid phosphate . . 


. 900 containing phos. acid . 


. 126.0 


6.30 


Sulphate of potash , 


, 450 containing potash . . 


. 225.0 


11.50 


Plaster, etc. . . 


. 400 







3L0 


I-5S 


210.0 


10.50 


75.0 


5-75 



292. Fertilizers and Tillage. — Commercial fertilizers 
cannot be made to take the place of good tillage, which 
is equally as important when fertilizers are used as when 



COMMERCIAL FERTILIZERS AND THEIR USE 245 

they are omitted. Scant crops are as frequently due to 
the want of proper tillage as to the absence of plant 
food. Poor cultivation results in getting the soil out of 
condition ; then, instead of thoroughly preparing the 
land, commercial fertilizers are resorted to, and the 
conclusion is reached that the soil is exhausted, when in 
reality it is suffering for the want of cultivation, for a 
dressing of land plaster, for farm manures, or for a 
change of crops. There is no question but what Better 
tillage, better care and use of farm manures, culture of 
clover and systematic rotation of crops would result in 
greatly reducing the amount annually spent for com- 
mercial fertilizers, without reducing the yield of crops, 
as well as securing larger returns for the fertilizers used. 
In general, the better the cultivation the less the amount 
of commercial fertihzer required for average farm crops. 
Cultivation cannot, however, entirely take -the place of 
fertilizers. 

293. Abuse of Commercial Fertilizers. — When a soil 
produces poor crops, a complete fertilizer is frequently 
used where only an amendment is needed. Restricted 
crop production on long-cultivated prairie soils is often 
due to poor physical condition, deficiency of humus and 
availalDle nitrogen, or, in some cases, to lack of a mineral 
element as potash or phosphoric acid. If the nitrogen 
is supplied by legumes, and the one element of fertility 
needed is added, improved cultivation together with the 
chemical action of the humus on the minerals of the soil 



246 SOILS AND FERTILIZERS 

will generally furnish the necessary, available plant 
food. Instead, however, of providing the one element 
needed, others which may already be present in the soil 
in liberal amounts are often supplied at an unnecessary 
expense, instead of being made available by cultivation. 
Another abuse of fertilizers is their application to the 
wrong crop. A heavy application of potash fertilizer to 
a wheat crop grown on a rich clay soil, or of nitrate of 
soda on land seeded to clover, or of land plaster to flax 
grown on a limestone soil, would be a waste of money. 

294. Judicious Use of Fertilizers. — In order to make 
the best use of commercial fertilizers, both the soil and 
the crop must be carefully considered. All soils do not 
alike respond to commercial fertilizers, and farm crops 
possess different powers of assimilating food ; turnips, 
for example, have very restricted power of phosphate 
assimilation, hence they require phosphate manures, and 
wheat may need help in obtaining its nitrogen. A 
wheat crop will starve for want of nitrogen, while an 
adjoining corn crop will scarcely feel its need. Wheat 
has strong power of assimilating potash, while clover 
has less. Hence in the use of fertilizers the ability of 
the plant to obtain its food must be considered. A 
light application of either a special purpose or a com- 
plete fertilizer at the time of seeding is often advanta- 
geous, as it encourages plant growth by supplying food 
when it is most needed. There should be some at this 
time in a highly available condition for the use of the 



COMMERCIAL FERTILIZERS AND THEIR USE 



247 



young plants, after that stored up in the seed has been 
exhausted, and before they are strong enough to make 
available their own food. 



Fig. 45. Wheat Plots fertilized in Different Ways. 

(From left to right.) 

Complete Fertilizer (Com.), Phosphate Fertilizer, P. 

Potash Fertilizer, K. Nitrogen Fertilizer, N. 

No Fertilizer, Check. 

Commercial fertilizers may assist in promoting desir- 
able bacterial changes in soils resulting in the elabo- 
ration of plant food. Before they are used, however, 
careful field trials should be made. 



295. Experimental Plots. — A piece of land well tilled 
and of uniform texture should be used for field trials 



248 



SOILS AND FERTILIZERS 



1 



with fertilizers. After preparation for the crop, small 
plots 1/20 of an acre are staked off. A convenient size 
is, length 204 feet, width 10 feet 8 inches, area 2176 
square feet. Between each plot a strip 3 feet wide is 
left. The plan is to apply one element or a combina- 
tion of elements to a plot and compare the results with 
plots differently treated.'^'^ 

296. Preliminary Trial. — It is best to make a prelim- 
inary trial one year and verify the conclusions the next. 
In making the tests, eight plots are necessary and fer- 
tilizers are applied in the following way : 

The first plot receives no fertilizer and is used as the 
basis for comparison. 

The second plot receives a dressing of 8 pounds nitrate 
of soda, 16 pounds acid phosphate, and 8 pounds sul- 
phate or muriate of potash. 

The third plot receives nitrogen and phosphoric 
acid. 

The fourth plot receives nitrogen and potash. 

The fifth plot receives nitrogen. 

The sixth plot receives phosphoric acid and potash. 

The seventh plot receives potash. 

The eighth plot receives phosphoric acid. 



No fertilizer 


N 


N 


N 




P2O5 


P-iOs 


K.2O 




KoO 






I 


2 


3 


4 



COMMERCIAL FERTILIZERS AND THEIR USE 



249 



N 


P2O5 
K2O 


KoO 


P2O5 


5 


6 


7 


8 



Should good results be obtained on plot No. 3, the 
indications are that there is a deficiency of the two 
elements, nitrogen and phosphoric acid. An increased 
yield from No. 4 indicates deficiency of nitrogen and 
potash. Under such conditions the use of a complete 
fertihzer would be unnecessary. If No. 5 gives an ad- 
ditional yield, the soil is in want of nitrogen. From 
the eight plots it will be seen which of the various ele- 
ments it is advisable to use. The fertilizers should be 
applied after the land has been thoroughly prepared and 
before seeding. Corn is a good crop for the first trial. 
The number of plots may be increased by using well- 
prepared stable manure and gypsum on plots 9 and 10, 
respectively. The second year the results should be 
verified. 



297. Deficiency of Nitrogen. — If the results indicate 
a deficiency of nitrogen, select two crops, one as wheat, 
which is particularly benefited by dressings of nitrogen, 
and another as corn which has less difficulty in obtain- 
ing this element. The cultivation of each crop should 
be that which experience has shown to be the best. On 
one wheat and one corn plot 8 pounds of nitrate of 
soda should be used, a plot each of wheat and corn being 



250 SOILS AND FERTILIZERS 

left unfertilized. If both the corn and the wheat are 
benefited by the nitrogen, the soil is in need of this ele- 
ment. If, however, the wheat responds and the corn 
does not, the soil is not in great need of nitrogen, but 
does not contain an abundance in available forms. ' 

298. Deficiency of Phosphoric Acid. — In experiment- 
ing with phosphoric acid, turnips are grown on two 
plots and barley on two plots. To one plot of each, 16 
pounds of acid phosphate are applied. If both crops 
show additional yields, the soil is in need of available 
phosphoric acid. If only the turnips respond while the 
barley is indifferent, the soil contains a fair amount. 
Barley and turnips are used because there is such a 
marked difference in their power to assimilate phosphoric 
acid. 

299. Deficiency of Potash. — In order to determine the 
condition of the soil as to potash, potatoes and oats 
may be used as the trial crops, and 8 pounds of sulphate 
of potash should be applied to one plot of each. Addi- 
tional yields indicate a poverty of available potash ; an 
increased potato crop and an indifferent oat crop indicate 
potash not in the most available form. If no additional 
yields are obtained with either crop, the soil is not in 
need of potash. 

300. Deficiency of Two Elements. — If the preliminary 
trial indicates a deficiency of two elements, as nitrogen 
and phosphoric acid, in verifying these results, both 



COMMERCIAL FERTILIZERS AND THEIR USE 2$! 

elements are used together, in the same way as de- 
scribed for deficiency of nitrogen, with additional plots 
for the separate application of nitrogen and phosphoric 
acid. 

301. Importance of Field Trials. — While it is a diffi- 
cult matter to determine the actual needs of a soil, it 
will be found that both time and money are saved by a 
systematic study of the question. Suppose fertilizers 
are used in a ' hit or miss ' way year after year on a 
soil deficient only in phosphoric acid, it might take eight 
years to indicate what the soil really lacks if a different 
fertilizer is used each year, and during all this period 
either the soil fails. to receive its proper fertilizer, or 
expensive and unnecessary plant food is provided. 
Field tests to be of value must be continued for a num- 
ber of years and the results verified. 

302. Will it pay to use Commercial Fertilizers? — 

This question can be answered only by trial. If a soil 
is in need of available plant food, the additional yield 
should pay for the fertihzer and the expense of using 
it. Some fertilizers have an influence on two or three 
successive crops, and only partial returns are received 
the first year. When large crops must be produced on 
small areas, as in truck farming, commercial fertilizers 
are generally necessary. They have not yet been ex- 
tensively used in the western prairie states in the pro- 
duction of large tracts of staple crops, as wheat and corn. 



252 SOILS AND FERTILIZERS f 

If there is a good stock of natural fertility in the soil 
and it is well tilled, with farm manures used and the 
crops systematically rotated, commercial fertilizers will 
not be needed. With poor cultivation and a soil that 
has been impoverished by injudicious cropping, they 
are necessary. Commercial fertilizers sometimes fail 
to give good results because of an excessively acid or 
alkaline condition of the soil. 

303. Amount of Fertilizer to use per Acre. — When 
commercial fertilizers are used in general farming, just 
enough should be applied to produce normal yields. 
Heavy applications at long intervals are not so pro- 
ductive of good results as light applications more fre- 
quently. From 400 to 600 pounds per acre is as much 
as should be used at one time unless previous trials 
have shown that heavier applications are necessary. 
The way in which the fertiHzer is to be applied, as 
broadcast or otherwise, must be determined by the crop 
to be grown. The fertilizer should not come in contact 
with seeds, neither should it be plowed under nor worked 
into the soil to such a depth that it may be lost by leach- 
ing before it can be appropriated by the crop. 

304. Excessive Applications of Fertilizers Injurious. — 

An overabundance of plant food has an injurious effect 
upon crop growth. Plants take their food from the soil 
in dilute solutions, and when the solution is concentrated 
abnormal growth results. Potatoes heavily manured 



COMMERCIAL FERTILIZERS AND THEIR USE 253 

with nitrate of soda produce luxuriant vines, but only 
a few small tubers. When a medium dressing is used 
along with potash and phosphoric acid, a more balanced 
growth and better yield result. 

Heavy applications of nitrate of soda produce a rank 
growth of straw, with a low yield of grain. The excess 
of nitrogen causes the mineral matter to be utilized for 
straw and leaves only a small amount for grain produc- 
tion. When applications of commercial fertilizers are 
too heavy, plants take up unnecessary amounts of food 
and fail to make good use of it. In fact, crops may be 
overfed, or fed an unbalanced ration, the same as ani- 
mals. Hence in the use of fertilizers excessive and un- 
balanced applications are to be avoided. 

305. Fertilizing Special Crops. — There are crops 

which need special help in obtaining some one element, 

and in using fertilizers the rule should be to help those 

crops which have the greatest difficulty in obtaining 

food. When the soil does not show a marked defi- 

1 ciency in any one element, light dressings of special 

I purpose manures may be made to the following crops : 

, Wheat. — Nitrogen first, then phosphoric acid. In 

1 the case of some soils, phosphoric acid and potash pro- 

1 duce larger yields than nitrogen. 

j Barley, oats, and rye require manuring like wheat, but 
I to a less extent. Each crop has a different power of 
1 assimilating nitrogen. Wheat requires the most help 
t and barley and rye the least. 



254 SOILS AND FERTILIZERS 

Corn. — Phosphoric acid first, then nitrogen and 
potash. 

Potatoes. — General manuring, reenf orced with pot- 
ash. 

Mangels. — Nitrogen. 

Tiirnips. — Phosphoric acid. 

Clover. — Lime and potash. 

Timothy. — General manuring. 

306. Commercial Fertilizers and Farm Manures. — 

Commercial fertilizers should not replace farm manures, 
but simply reenforce them. Although commercial fer- 
tilizers are called complete manures, they fail to supply 
organic matter. It is more important in some soils 
than in others that the organic matter be maintained, 
because in some soils the organic matter takes a more 
important part in crop production than does the food 
applied in commercial forms. When a rich prairie soil 
is reduced by grain cropping and is allowed to return to 
pasture, heavier yields of grain are afterward obtained 
than from similar land which has received only appli- 
cations of commercial fertilizers. This is due to the 
action of the humus in the soil. At the Canadian Do- 
minion Experimental Farms, where comparative trials 
have been made for eighteen years with farm manures 
and commercial fertilizers, it has been found that farm 
manures, even on new lands, give better results than 
commercial fertilizers for the production of wheat and 
corn.^^ 



CHAPTER XI ■ 

FOOD REQUIREMENTS OF CROPS 

307. Amount of Fertility removed by Crops. — The 

amount of fertility removed from an acre of soil pro- 
ducing average crops varies between wide limits. For 
example, an acre of mangels removes 150 pounds of 
potash, while an acre of flax removes 27 pounds ; an 
acre of corn removes 75 pounds of nitrogen, while 
an acre of wheat removes 35 pounds. Crops which 
remove the most fertility do not always require the most 
help in obtaining their food. This is because the 
amount of plant food assimilated is not a measure of 
the power of crops to obtain food. An acre of corn 
requires over twice as much nitrogen as an acre of 
wheat, but wheat often leaves the soil in a more im- 
poverished condition than corn, because corn has greater 
power to procure nitrogen and utilize that formed by 
nitrification after the wheat crop has completed its 
growth'. The available nitrogen if not utilized by a crop 
may be lost in various ways. Mangels require twice as 
much phosphoric acid as flax, but are a strong feeding 
crop and need less help in obtaining this element. It 
was formerly beheved the plant food in the matured 
crop indicated the kind and amount of fertilizing ingredi- 
ents to apply, and that a correct system of manuring 

255 



256 



SOILS AND FERTILIZERS 



required a return to the soil of all elements removed in 
the crop. Experiments show this view to be incorrect. 

Pounds per Acre of Plant Food removed by Crops ^^ 



Crops 


Gross 
weight 


Nitro- 
gen 


Phos- 
phoric 
acid 


Potash 


Lime 


Silica 


Total 
ash 


Wheat, 20 bu. . . 


1200 


25 


12.5 


7 


I 


I 


25 


Straw . . 






2000 


ID 

35 


7-5 
20 


28 

35 


7 


115 
116 


185 


Total . 




210 


Barley, 40 bu. 






1920 


28 


15 


8 


I 


12 


40 


Straw . . 






3000 


12 


5 


30 


8 


60 


176 


Total . 








40 


20 


38 


9 


72 


216 


Oats, 50 bu. 






1600 


35 


12 


10 


1-5 


15 


55 


Straw . . 






3000 


15 

50 


6 
18 


35 

45 


9-5 

II.O 


60 


150 
205 


Total . 


75 


Corn, 65 bu. 






2200 


40 


18 


15 


I 


I 


40 


Stalks . . 






3000 


35 

75 


2 
20 


45 
60 


II 
12 


89 
90 


160 
200 


Total . 




Peas, 30 bu. 






1800 




18 


22 


4 


I 


64 


Straw . . 






3500 


— " 


7 

25 


38 
60 


71 

75 


9 
10 


176 


Total . 




240 


Mangels, 10 tons . 


20000 


75 


35 


150 


30 


10 


350 


Meadow hay, i ton 


2000 


30 


20 


45 


12 


50 


175 


Clover hay, 2 tons . 


4000 




28 


66 


75 


15 


250 


Potatoes, 150 bu. . 


9000 


40 


20 


75 


25 


4 


125 


Flax, 15 bu. . . . 


900 


39 


15 


8 


3 


0.5 


34 


Straw 


1800 


15 


3 


19 


13 


3 


53 


Total . . . 





54 


18 


27 


16 


3-5 


87 



FOOD REQUIREMENTS OF CROPS 257 

For example, an acre of wheat contains 35 pounds of 
nitrogen, while an acre of clover contains 70 pounds ; 
if 70 pounds of nitrogen were applied to an acre of 
clover and 35 pounds to an acre of wheat, poor results 
would follow, because clover can obtain its own nitrogen 
while wheat is less able to do so, and the 35 pounds 
would not necessarily come in contact with the roots 
so that all could be assimilated. While the amount of 
plant food removed in crops cannot serve as the basis 
for their manuring, valuable results are obtained from a 
study of the different elements of fertihty which they 
contain. In making use of the preceding table, other 
factors, as the influence of the crop upon the soil and 
the power of the crop to obtain its food, must also be 
considered. 

308. Plants exert a Solvent Power in Obtaining 

Food. — It is believed that crops procure some of their 

food from minerals insoluble in water. Experiments 

j by Liebig demonstrate that plants have the power of 

I rendering a portion of their food soluble, provided it 

; does not exist in forms too inert to undergo chemical 

change. Liebig grew barley in boxes so constructed 

j that all of the water-soluble plant food could be secured. 

I Two of the boxes were manured and two left unmanured. 

In one box which received manure and one which 

I received none, barley was grown. One each of the 

I manured and unmanured boxes was left barren. He 

I collected all of the drain waters and determined the 



258 SOILS AND FERTILIZERS 

soluble mineral matter present, also weighed and analyzed 
the plants. His results showed that 92 per cent of the 
potash was obtained from forms insoluble in waterJ^ 

The soluble plant food from a fertile soil is not gen- 
erally sufficient for plant growth,^^ When oats, wheat, 
and barley were seeded in prepared sand and watered 
with the teachings from a pot of fertile soil, they made 
only a limited growth. Oats grown in prepared sand 
and watered with soil teachings assimilated only 25 per 
cent as much phosphoric acid as plants grown in fertile 
soil. See Section 224. The character and concentra- 
tion of the soil solution are, however, important factors 
in crop production and some soils may contain sufficient 
amounts of water-soluble elements to produce crops. The 
relative amounts of food which plants take from the 
soil solution and that which they render soluble have 
not been extensively investigated. 

In the roots of plants there are various organic acids 
and salts. Between the root and the soil is a layer of 
water. The plant sap and the soil water are separated 
by plant tissue, which serves as a membrane. All of the 
conditions are favorable for osmosis. The sap from the 
roots finds its way into the soil in exchange for some of 
the soil water. The acid and other compounds, excreted 
by the roots, act upon the mineral matter, rendering 
portions of it soluble, and then it is taken up by the 
plant. Different plants contain different kinds and 
amounts of solvents, as well as present different areas of 
root surface to act upon the soil, and the result is that 



FOOD REQUIREMENTS OF CROPS 259 

agricultural crops have different powers of assimilating 
food. This action of living plant roots upon soils is a 
digestion process which is somewhat akin to the diges- 
tion of food by animals. 

Plants not only possess the power of rendering a por- 
tion of their food soluble, but they are also able to select, 
and to reject that which is unnecessary. For example, 
wheat grown on prairie soil with soda in equally abun- 
dant and soluble forms as the potash will contain 
relatively little soda compared with the potash ; also 
many seaweeds contain more potash than soda, although 
the sea water in which they grow has an excess of 
sodium salts. 

For the feeding of crops, a nutritive soil solution is 
desirable, and the soil should have a good stock of 
reserve material that can be utilized either by action of 
the plant roots or readily pass into solution in the soil 
water. 

CEREAL CROPS 

309. General Food Requirements. — Cereal crops con- 
tain a high per cent of silica and evidently possess the 
power of feeding upon some of the simpler silicates of 
the soil,'''* liberating the base elements and using them as 
food, while the silica is deposited in the outer surface of 
the straw. As previously stated, cereal crops, although 
they do not remove large amounts of total nitrogen from 
the soil, require special help in obtaining this element. 
There is, however, a great difference among the cereals as 



260 SOILS AND FERTILIZERS 

to power of assimilating nitrogen. Next to nitrogen they 
stand most in need of phosphoric acid. There exists in 
many soils a greater deficiency of available phosphoric 
acid and potash than of nitrogen, although, in general, 
cereal crops are better able to procure these elements 
than they are nitrogen. The humic phosphates are 
utilized by nearly all the cereals. 

310. Wheat. — This crop is more exacting in its food 
requirements than barley, oats, or rye. It is compara- 
tively a weak feeding crop, and the soil should be in a 
higher state of fertihty than for other grains. The ex- 
tensive experiments of Lawes and Gilbert give valuable 
information regarding the effects of manures on wheat. 
Their results are given in the following table '.'^ 



Average Yield of Wheat per Acre 






Bushels 


No manure for 40 years 


14 

i5i 

231 

321 

36i 
32i 


Minerals alone for 32 years 


Nitrogen alone for 32 years 

Farmyard manure for 32 years 

Minerals and nitrogen for 32 years ^ 

Minerals and nitrogen for 32 years ^ 



^86 pounds of nitrogen as sodium nitrate. 
*86 pounds of nitrogen as ammonium salts. 



The food requirements of wheat are such that it should 
be given a favored position in the rotation. It may follow 
clover, provided the clover sod is light and is fall plowed. 



FOOD REQUIREMENTS OF CROPS 26l 

On some soils, however, wheat does not thrive following 
a sod crop, as it takes nearly a year for a heavy sod 
residue to get into suitable food forms for a wheat crop, 
and under such a condition, oats should first be sown, 
then wheat may follow. On average soil, a medium 
clover sod, plowed late in summer or in early fall, and 
followed by surface cultivation, leaves the land in good 
condition for spring wheat. It is not advisable to have 
wheat follow barley, because the soil will be too porous, 
and barley being a stronger feeding crop leaves the land 
in a poor state as to available plant food. When corn 
has been well manured, wheat may follow. The food re- 
quirements of wheat are best satisfied following a light, 
well-cultivated clover sod, or following oats, which have 
been grown on heavy sod, or following corn that has 
been well manured. When wheat is judiciously grown 
in a rotation and farm manures are used, it is not an ex- 
hausting crop. Light dressings of farm manure may 
be used on land that is being prepared for wheat. On 
many western prairie soils, dressings of phosphate and 
potash, either alone or in combination, materially increase 
the yield and improve the quahty of the crop. Potash 
fertilizers have a tendency to produce strong bright 
j straw that is more resistant to fungous diseases. Nitro- 
I gen alone does not give as good results as when com- 
bined with minerals. 

311. Barley. — While wheat and barley belong to the 
same general class of cereals, they differ greatly in their 



262 SOILS AND FERTILIZERS 

habits and food requirements. Barley is a stronger 
feeding crop, has greater root development near the 
surface, and can utilize food in cruder forms. In many 
of the western states, soils which produce poor wheat 
crops, from too long cultivation, give excellent yields of 
barley. This is due to changed conditions, of both the 
chemical and mechanical composition of the soil. Long 
cultivation has made the soil porous, and reduced the 
nitrogen content. Barley thrives best on a rather open 
soil, and has greater nitrogen assimilative power than 
wheat. Barley, however, responds liberally to manur- 
ing, particularly to nitrogenous manures. The experi- 
ments of Lawes and Gilbert on the growth of barley are 
briefly summarized in the following table : "^^ 

Average Yield of Barley per Acre for 34 Years 



No manure 

Superphosphate alone 

Mixed minerals 

Nitrogen alone 

Nitrogen and superphosphate 

Farmyard manures 

312. Oats. — Oats can obtain food under more ad- 
verse conditions than either barley or wheat. They are 
also less exacting as to the physical condition of the 
soil. The oat plant will adapt itself to either sandy or 
clay soil, and will thrive in the presence of alkaline 




FOOD REQUIREMENTS OF CROPS 263 

matter or humic acid where wheat would be destroyed. 
In a rotation, oats usually occupy a position less fa- 
vored by manures ; they are, however, greatly benefited 
by fertilizers, particularly those of a nitrogenous 
nature. The oat crop responds liberally to manuring. 
Light dressings of farm manure can be applied directly 
to oat land when well worked into the soil before 
seeding. 

313. Corn. — Experiments with corn indicate that 
under ordinary conditions it requires most help in 
obtaining phosphoric acid. Corn removes a large 
amount of gross fertility, and if its production is long- 
continued without the use of manures it impoverishes 
the soil. Its habits of growth, however, are such that it 
generally leaves an average prairie soil in better me- 
chanical condition for succeeding crops. Corn is not 
injured as are many grain crops by heavy applications 
of stable manure, and does not, like flax, produce waste 
products which are destructive to itself. The conditions 
I are better for wheat culture after one or two corn crops 
j have been removed from rich, newly broken prairie soil. 
! The food requirements of corn are satisfied by applica- 
1 tions of stable manure, occasionally reenforced with 
S a little nitrogen and phosphoric acid, and in the case of 
some soil potash. After clover, corn gives excellent 
ij returns, and when corn is the chief market crop it 
, should be favored by having the best position in the 
ii rotation. 



264 SOILS AND FERTILIZERS 



MISCELLANEOUS CROPS 



314. Flax is very exacting in food requirements and 
for its culture the soil must be in a high state of fertility. 
It is a type of weak feeding crop. There are but few 
roots near the surface and consequently it has restricted 
power of nitrogen assimilation.^^ Flax should be in- 
directly manured. Direct applications of stable manure 
produce poor crops, but when the manure is applied to 
the preceding crop, excellent results are obtained. Flax 
does not remove a large amount of fertility, but if 
grown too frequently the tendency is to get the land out 
of condition, rather than to exhaust it. The best condi- 
tions for flax culture require that it should be grown on 
the same land only once in five years. Flax straw does 
not form suitable manure for flax lands. Dr. Lugger 
demonstrated that there are produced, when the roots 
and straw of flax decay, products which are destructive 
to succeeding flax crops.'^'' Also flax diseases are intro- 
duced into land by the use of diseased flax seed. The 
food requirements of flax are met when it follows corn 
which has been well manured, or a sod which has been 
given the cultivation described for wheat. Flax and 
spring wheat are much aHke in food requirements. 

315. Potatoes. — Potatoes are surface feeders, and ] 
when grown continuously upon the same soil without , 
manure, the yield per acre decreases more rapidly than i 
that of any other farm crop. Experiments with pota- I 



FOOD REQUIREMENTS OF CROPS 



265 



toes by Lawes and Gilbert, using different manures, 
gave the following results:'^ 

Average Yield per Acre for 12 Years 



Tons 



CwT. 



No manure 

Superphosphate 

Minerals alone 

Nitrate of soda alone . . . 
Mixed manures and nitrogen . 
Farm manures, alternate years 



I 


19I 


3 


5 


3 


71 


2 


41 


5 


171 


4 


3l 



Potatoes require liberal general manuring reenforced 
with wood ashes or other potash fertilizer. In the rota- 
tion they should follow grain or pasture, provided the 
fertility of the soil is kept up. Commercial fertilizers 
for potato production should contain a fair amount of 
! available nitrogen (2 to 3 per cent) and a more liberal 
i supply of phosphoric acid and potash. See Section 

324- 
I 

i 316. Sugar Beets. — This crop is more exacting in its 
j food requirements than any other root crop. Excessive 
': fertility is not conducive to a high content of sugar. 
* Soils in good mechanical condition and medium state 
of fertility usually give the best results.'^ Sugar beets 
! should not receive heavy dressings of stable manure, 
' because an abnormal growth results. Nitrogenous fer- 
tilizers may be applied only in limited amounts, heavier 



266 SOILS AND FERTILIZERS 

dressings of potash and phosphoric acid are admissible. 
When sugar beets follow corn which has been manured, 
or grain which has left the soil in an average state of 
fertility, and a medium dressing of commercial fertilizer is 
applied, the food requirements of the crop are well met. 

317. Roots. — Mangels are gross feeders and re- 
move a larger amount of fertility from the soil than 
any other farm crop."* When fed to stock and the 
manure is returned to the soil, they materially aid in 
making the plant food more available for dehcate- 
feeding crops. Mangels are better able to obtain phos- 
phoric acid than are turnips and need the most help 
in the way of nitrogen. Turnips are surface feeders 
with stronger power of nitrogen assimilation than the 
grains, but with restricted power of phosphate assimi- 
lation. Manures for turnips should be phosphatic in 
nature. 

318. Rape is a type of strong feeding plant capa- 
ble of obtaining its food under conditions adverse to 
grain crops. When grown too frequently upon the 
same soil, it does not thrive. On account of its great 
capacity for obtaining food, it is a valuable crop to 
use for green manuring purposes.^^ Farm manure is 
the most valuable fertilizer for rape. 

319. Buckwheat is a strong feeding crop, and its 
demands for food are easily met. On rich soil, a rank 
growth of straw results, with poor seed formation. 



FOOD REQUIREMENTS OF CROPS 26/ 

Buckwheat is usually sown upon the poorest soil of the 
farm. Because it is a strong feeder it is frequently 
used as a manurial crop, being plowed under while 
green to serve as food for weaker feeding crops. On 
poor soils a moderate use of mineral fertilizers and a 
small amount of nitrogen are beneficial. 

* 320. Cotton. — On average soils cotton stands in need 
first of phosphoric acid and second of nitrogen.^i It is 
most able to obtain potash. Organic nitrogen as cot- 
tonseed meal and stable manure appear equally as 
effective as nitric nitrogen. Phosphoric acid must be 
applied in the most available forms, although the crop 
uses but little. The fertihzers should be drilled in at the 
time of planting. The use of green manuring crops as 
cowpeas, with an application of marl, gives beneficial re- 
sults. Marl, which is composed mainly of calcium car- 
bonate, combines with the acids formed from the decay 
' of the vegetable matter and as a result the plant food of 
the soil is made more available, which is beneficial to 
1 both soil and crop. There are but few crops which 
] respond so readily to fertilizers as cotton. It does 
' not remove a large amount of fertility, but when not 
I systematically grown in a rotation exhausts the soil 
] in the same way as when grain is grown continuously. 

321. Hops. — The hop plant is exacting in its food 
I requirements. An excess of easily soluble plant food is 
I injurious, while a lack is equally so. An abundance of 



268 SOILS AND FERTILIZERS 

food in organic forms is most essential. Heavy dressings 
of farm manures may be applied. Where hops are 
grown there is a tendency to use all the manure on 
the hops, while the rest of the farm is left unma- 
nured. Very light applications of commercial fertili- 
zers may be used in connection with stable manure, 
but such use should be made only after a preliminary 
trial on a small scale. 

322. Hay and Grass Crops. — Most grass crops have 
shorter roots than grain crops ; they are surface feeders 
and not so able to secure mineral food. When a num- 
ber of crops have been removed, the soil may stand in 
need of available mineral matter. Farm manures are 
particularly well adapted for fertilizing grass. Applica- 
tions of nitrogenous manures result in discouraging the 
growth of clover. Heavy manuring of grass land has a 
tendency to reduce the number of species, and one kind 
is apt to predominate.^^ On some soils ashes, and on 
others lime fertilizers, have been found very beneficial. 
The manuring of grass must be varied to meet the needs 
of different soils. Permanent meadows require different 
manuring from meadow introduced as an important crop 
in the rotation. Permanent meadows should receive an 
annual dressing of farm manure or of a commercial fer- 
tilizer containing phosphoric acid, potash, and a fair 

amount of nitrogen. ! 

* I 

323. Leguminous Crops. — For leguminous crops | 
potash and lime fertilizers have been found of special 



«< 



FOOD REQUIREMENTS OF CROPS 269 

value. Analyses of clover and peas show large amounts 
of both potash and lime. In some cases an application of 
phosphate fertilizer is necessary before a crop of clover 
can be secured. Farm manure on sandy or heavy clay 
soils will materially assist in the production of clover. 
Sometimes clover fails when grown too frequently upon 
the same soil, not because the soil is exhausted but be- 
cause of the development in the soil of organic products 
which are destructive to growth. As the result of grow- 
ing leguminous crops, the food requirements of which 
are inexpensive, the soil is enriched with nitrogen, and 
the phosphoric acid is changed to available forms. 

324. Garden Crops. — For general garden purposes, 
there should be a liberal supply of plant food. Well- 
composted farm manure can advantageously be reen- 
forced with commercial fertilizers. A liberal use of 
manure insures not only the maximum yield, but crops 
of the best quality. Maturity of crops also is influenced 
by fertilizers. 

Voorhees^^ recommends as a fertilizer for general gar- 
den purposes one containing : 





Per Cent 


Nitrogen 


4.00 
8.00 


Phosphoric acid 


Potash 


10.00 







This and similar fertilizers can be applied at the rate 
of 1000 pounds per acre. To meet the requirements 



2/0 SOILS AND FERTILIZERS 

of special crops, as spinach and cabbage, an additional 
dressing of nitrate of soda may be used. Asparagus 
should preferably be fertilized after harvesting the 
crop, so as to encourage new growth and the storing 
up of reserved building material in the roots for next 
year's growth. 

For early maturing garden crops, a fair but not ex- 
cessive amount of nitrogen should be applied; also a 
liberal supply of phosphates will be found advantageous. 
Some garden crops, as cucumbers, pumpkins, and squash, 
thrive best when their food is in organic forms, as the 
humate compounds derived from farm manures. A 
continuous supply of available plant food is thus fur- 
nished to the growing crop. Onions are benefited by 
a generous dressing of soluble nitrogen. Celery also 
should be well supplied with soluble nitrogen combined 
with soluble forms of mineral food. Tomatoes require 
general fertilizing ; for early maturity, nitrogen, as 
nitrate of soda, is beneficial, but an excess should be 
avoided ; for late maturity, farm manures and com- 
mercial fertilizers containing less nitrogen may be 
used. For general garden purposes, a complete fer- 
tilizer is preferable to an amendment, as a better bal- 
anced growth is secured which favorably affects both 
the yield and the quahty. 

325. Fruit Trees. — In the manuring of fruit trees, 
the first object is to produce thrifty trees, as subsequent 
fertilizing for fruit will not give satisfactory results with 



FOOD REQUIREMENTS OF CROPS 27I 

poorly grown and partially developed trees. In order 
to promote growth, a liberal supply of a complete ferti- 
lizer should be used, and the soil should be kept in the 
best mechanical condition. When an orchard is in full 
bearing, there is as heavy a draft upon the soil as when 
a wheat crop is grown.^ To meet this, farm manures 
and commercial fertilizers should be used liberally. 
The productive period of an orchard is materially 
lengthened by judicious use of fertilizers. The quality 
of the fruit is often, adversely affected by a scant supply 
of plant food. A quick acting fertilizer, containing 
kainit, nitrate of soda, and dissolved phosphate rock, 
should be used in the spring, followed if necessary by 
a light dressing of some manure which yields up its 
fertility more slowly. An excess of nitrogen, however, 
should be avoided. Stone fruits are benefited by the 
addition of lime to the fertilizer. Lime fertilizers impart 
hardiness to fruit trees. 

I 326. Small Fruits. — On account of the comparatively 
I limited bearing period of small fruits, the land should 
} be brought to a high state of productiveness and 
! good physical condition by liberal use of farm manures 
(previous to planting. Quick acting fertihzers are the 
' most suitable for small fruits. Dressings of nitrate of 
soda, 50 to 100 pounds per acre, can be applied early in 
^the season to promote leaf activity. This should be 
I followed by an application of a general fertihzer con- 
taining about 3 per cent of available nitrogen, 8 per 



2/2 SOILS AND FERTILIZERS 

cent of phosphoric acid, and lO per cent of potash. 
The amount used should range from 200 to 400 pounds 
per acre until the character and needs of the soil are 
determined. It will often be found that large amounts 
can be used economically. 

327. Lawns. — In making a lawn, a mixture of six 
parts of bone ash , two parts of muriate of potash, and 
one part of nitrate of soda can be applied at the rate of 
5 to 7 pounds per square rod prior to seeding. A good 
lawn should have a subsoil that is fairly retentive of 
moisture, one containing 10 to 15 per cent of clay or'| 
a large amount of fine silt. Too much potash and; 
lime encourage exclusive growth of clover and crowd- 
ing out of grasses. During the season, two or three! 
applications can be made of a commercial fertilizer 
containing about 3 per cent of nitrogen, 10 per cent 
of phosphoric acid, and 3 per cent of potash, at the 
rate of one pound per square rod. When part of the| 
nitrogen is in the form of nitrates and part as ammo-t 
nium salts, better results are secured than when thei 
nitrogen is all in one form. It is also advisable to) 
supply the phosphoric acid in more than one form. 
An even application of fertilizer to a lawn is quite 
necessary, otherwise the growth is "patchy." Hard 
wood ashes evenly spread at the rate of i to 2 pounds) 
per square rod and reenforced with nitrate of soda cacj 
be used advantageously as a lawn fertilizer. 



CHAPTER XII 

ROTATION OF CROPS AND CONSERVATION OF SOIL 
FERTILITY 

328. Object of Crop Rotation. — The object of system- 
atic rotation of crops is to conserve the fertihty of the 
soil and at the same time to produce maximum yields. 
In order to accomplish this, the food requirements 
of different crops must be met by good cultivation 
and judicious manuring. Rotations must be planned 
according to the nature of the soil and the system of 
farming that is to be followed. For general grain 
farming a different rotation is required than for ex- 
clusive dairying. Whatever the nature of farming, the 
whole farm should gradually undergo a systematic ro- 
tation. If the farm is uneven in soil texture, different 
I rotations may be practiced on the various parts. There 
jis no way in which soils are more rapidly depleted of 
I fertility than by the continued culture of one crop. In 
I exclusive wheat raising, for example, the losses are not 
'confined to the fertility removed in the crop, but other 
losses occur as described in the chapter on nitrogen. 
iWhen wheat is systematically grown in alternation with 
'other crops, losses of nitrogen are reduced to the mini- 
imum. 

i T 273 



274 SOILS AND FERTILIZERS 

When remunerative crops can no longer be produced, 
the soil is said to be exhausted. Soil exhaustion may 
be due either to a lack of plant food, to bacterial 
products, or to poor physical conditions arising from 
the soil being temporarily out of condition because of 
a one-crop system and poor methods of cultivation. 

329. Principles involved in Crop Rotation. — There 

are a few fundamental principles with which all rota- 
tions should conform. Briefly stated these are : 

1. Deep- and shallow-rooted crops should alternate. 

2. Humus-consuming and humus-producing crops 
should alternate. 

3. Crops should be rotated so as to make the best 
use of the preceding crop residue. 

4. Crops should be rotated so as to secure nitrogen 
indirectly from atmospheric sources and to promote 
desirable bacterial activities in the soil. 

5. Crops should be rotated so as to keep the soil in 
the best mechanical condition. 

6. In arid regions, crops should be rotated so as to 
make the best use of the soil water. 

7. An even distribution of farm labor should be se- 
cured by a rotation. 

8. Farm manures and fertilizers should be used in 
the rotation where they will do the most good. 

9. Rotations should be planned so as to produce 
fodder for stock, and so that every year there will be I 
some important crop to be sold. | 



ROTATION OF CROPS 275 

330. Deep- and Shallow-rooted Crops. — When deep- 
and shallow-rooted crops alternate, the draft upon the 
surface soil and subsoil is more evenly distributed and 
the physical condition of the soil is improved. In many 
soils, nitrogen and phosphoric acid are more abundant 
in the surface soil while potash and lime predominate 
in the subsoil. When such a condition exists the 
alternating of deep- and shallow-rooted crops is very 
beneficial, because the surface soil is gradually enriched 
by accumulations of fertility from the subsoil, deposited 
by decay of the residue of the deep-rooted crops, 

331. Humus-consuming and Humus-producing Crops. 

— When grain or hoed crops are grown continuously, 

oxidation of the humus occurs, and the chemical and 

physical properties of the soil are entirely changed by 

loss of the humus. The rotating of grass and grain 

crops and the use of stable manure serve to maintain 

the humus equilibrium. On some soils hme may be re- 

, quired along with the humus to prevent the formation 

( of humic acid, and in such cases the best conditions 

: exist when both lime and humus materials are supplied. 

Alternation of humus-producing and humus-consuming 

I crops is one of the essentials of a rotation. 

I 

I 332. Crop Residues. — Crop residues should always 

be placed at the disposal of weak feeding crops. After 

' a light clover and timothy sod, wheat or flax should 

j be grown in preference to barley or mangels. The 



2/6 SOILS AND FERTILIZERS 

weak feeding crop should be followed by a strong 
feeding crop, and then each is properly supplied with 
food. It would be poor economy, on an average 
soil, to follow clover and timothy with mangels, then 
with barley, and finally with flax, because the flax 
would be placed at a serious disadvantage following two 
strong feeding crops. If reversed, the crops would 
be placed in order of assimilative power, and the 
best use would be made of the sod-crop residue. 
When crops of dissimilar feeding habits follow each 
other, not only are the crop residues used to the best 
advantage, but the soil is relieved of excessive demands 
on special elements. For example, wheat and clover 
take different amounts of potash and lime from the 
soil. Wheat has the power of feeding upon silicates 
of potash which clover cannot assimilate, hence wheat 
and clover in rotation reheve the soil of excessive 
demands on the potash. 

333. Nitrogen-consuming and Nitrogen-producing Crops. 

— It is possible in a five-course rotation to maintain or 
even increase the nitrogen of the soil without the use 
of nitrogenous manures. In Section 145 an example 
is given of a rotation which has left the soil with a 
better supply of nitrogen than at the beginning. 
When a soil produces a good clover crop once in 
five years, and stable manure is used once during 
that time, the soil nitrogen is not decreased. Not only 
is nitrification influenced by cultivation and crop rota- 



ROTATION OF CROPS 2// 

tion, but other bacterial changes are also affected. The 
entire bacterial flora of a soil may be changed by 
modifications of systems of cultivation, cropping, and 
manuring. By means of rotating nitrogen-producing 
and nitrogen -consuming crops, grain can be sold from 
the farm without purchasing nitrogenous manures. 
Conservation of the nitrogen and humus of the soil 
is one of the most important points to consider in the 
rotation of crops. 

334. Influence of Rotation upon the Mechanical Con- 
dition of Soils. — With different kinds of crops the 
mechanical condition of soils is constantly undergoing 
change. Grain crops and hoed crops tend to make 
the soil open in texture. Grass crops have the opposite 
effect. All soils should undergo periodic compacting 
and loosening. Some require more of one treatment 
than of the other. In a rotation the action of the 
crop upon the mechanical condition of the soil should 
be considered, otherwise the soil may get into poor 
condition to retain water or become so loose that heavy 
losses occur through wind storms. Sandy soils are 
improved by methods of cropping which compact the 
soil, while heavy clays require the opposite treatment. 
The rotation should be made to conform to the re- 
quirement of the soil. 

335. Economic Use of Soil Water. — The rotation 
should not be of such a nature as to make excessive 



278 SOILS AND FERTILIZERS 

demands upon the soil water. For example, after a 
grain crop has been produced, it is best in regions of 
scant rainfall to plow the land and get it into condi- 
tion to conserve the water for the next year's crop, 
rather than to attempt to raise a catch crop the same 
year. During years of heavy rainfall catch crops may 
be grown for green manure to increase the humus con- 
tent of the soil. Crops removing excessive amounts 
of water should not be grown too frequently. Sun- 
flowers, for example, remove twenty times more water 
than grain crops, and cabbage removes more water 
than many other crops. With a good rotation and 
systematic cultivation a water balance may be carried 
in the soil from one year to the next, so that crops 
will be supplied in times of drought. 

336. Rotation and Farm Labor. — The rotation of 
crops should be so planned that there is an even 
distribution of farm labor. The importance of this is 
so plain that its discussion seems unnecessary. It 
is one of the most important points to consider in 
economic farming, and should not be lost sight of in 
planning rotations. 

337. Economic Use of Manures. — Farm manure 
should be applied to those crops which experience has 
shown to be the most benefited by its use. At least 
once during a five years' rotation the land should 
receive a dressing of stable or some other manure. 



ROTATION OF CROPS 



279 



When commercial fertilizers are used,, they should be 
applied to the crops which need the most help in 
obtaining food. With the growing of clover and the 
use of farm manures, the minimum amount of com- 




FlG. 46. A W'heat Field. This crop was grown on land where farm manure 
was used and a rotation of crops practiced. Ayer, Photographer. 

mercial fertilizer is required for general crop production. 
It is more economical to reenforce the farm manures 
with fertilizers especially adapted to the soil and crop 
than to purchase complete fertilizers for all crops. 

338. Salable Crops. — In all farming, something must 
be sold from the farm. It should be the aim to sell 



280 SOILS AND FERTILIZERS 

products which remove the least fertility, or if those 
are sold which remove large amounts, to return in 
cheaper forms the fertility sold. In a good rotation 
it is the plan to have at least one salable crop each 
year. The whole farm need not undergo the same 
rotation at the same time, and the rotation may be 
subject to minor changes, as circumstances require. 
To illustrate, wheat and flax occupy about the same 
position in a rotation. If at seeding time the indica- 
tions are that wheat will be a poor paying crop and 
flax command a high price, flax should be sown. The 
rotation should be such that one of two or three crops 
may be grown as circumstances require. A rotation 
should be reasonably flexible. 

339. Rotation Advantageous in Other Ways. — A good 
rotation will be found advantageous in other ways than 
those mentioned. With one line of cropping, land be- 
comes foul with weeds and insects which do not thrive 
when crops are rotated. Frequently the rotation must be 
planned so as to reclaim the land from weeds and rav- 
ages caused by insect pests. Many insects are capable 
of living only on a special crop ; when this crop is grown 
continuously on the same land the best conditions for in- 
sect ravages exist, and relief is secured only by rotation 
of crops. Fungous diseases also are most liable to occur 
on soils which produce annually the same crop, as the 
conditions are favorable for the propagation and hiber- 
nating of the disease-producing spores. 



ROTATION OF CROPS 28 1 

340. Long- and Short-course Rotations. — Rotations 
vary in length from 2 to 17 years. Long-course rota- 
tions are more generally followed in European and 
other of the older countries. The length of the rotation 
can be determined only by the conditions existing in 
different localities. As a general rule, long-course rota- 
tions should be attempted mainly on large farms and after 
a careful study of all of the conditions relating to the 
system of farming that it is desired to follow. For north- 
ern latitudes a rotation of four or five years gives excel- 
lent results. In some localities three-course rotations 
are the most desirable. 

A rotation that is suitable for one locality or kind of 
farming may be unsuitable for other localities and con- 
ditions. Because of variations in soil, climate, and rain- 
fall, no definite standard rotation can be proposed that 
will be applicable to all cases. 

341. Example of Rotation. — In deahng with the sub- 
ject of rotations it is best to take actual problems as 
they present themselves and plan rotations that will 
best meet all of the conditions. For example, a farm 
of 160 acres is to be rotated with the main object of 
producing fodder for five stock, and a small amount of 
grain for sale. To meet these requirements the rotation 
outUned on pages 282 and 283 is suggested. ^^ 

The farm is divided into eight fields of 20 acres each; 
seven fields are brought under the rotation, while one 
field is left free for miscellaneous purposes. Each year 



282 



SOILS AND FERTILIZERS 




ROTATION OF CROPS 



283 



















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284 SOILS AND FERTILIZERS 

there are produced 20 acres of corn, 20 acres of timothy 
and clover hay, 10 acres each of wheat and flax, 20 acres 
of barley, and 5 acres each of corn fodder, rye, peas, 
and potatoes, while 20 acres are reserved for pasture. 
The main income is derived from the sale of live stock 
and dairy products. 

Problems on Rotation 

1. Plan a rotation for general farming (160 acres), using the 
following crops : clover, timothy, barley, oats, potatoes, and corn. 
The soil is in an average state of fertility. Twenty-five head of 
stock are kept. 

2. Plan a three-course rotation for a sandy soil, the main object 
being potato culture. 

3. Plan a seven-year rotation for grain farming, using manure 
and a commercial fertilizer once during the rotation. The soil is 
a clay loam in a good state of fertility. 

4. Plan a rotation for general farming on a sandy loam. 

5. How would you proceed to bring an old grain farm from a 
low to a high state of productiveness ? Begin with the feeding of 
the stock. 

6. Using commercial and special purpose manures, how would 
you proceed to raise wheat, potatoes, and hay in a suitable rotation 
and continuously? 

7. Plan a rotation for a northern latitude, where corn cannot be 
grown, except for fodder, and where clover and timothy fail to 
do well; wheat and all small grains thrive, also millet, bromuS' 
inermis, rape, and some of the root crops. The soil is a clay loam, 
resting on a marl subsoil. Manure is very slow in decomposing. 
The rotation should be suited to general farming, wheat or flax 
being the important market crop. , 

8. Plan for a southern farm a rotation in which cotton forms an 
important part. 



CONSERVATION OF FERTILITY 285 

9. Plan a rotation for a market milk farm of 90 acres. One hun- 
dred head of stock are kept and mostly mill feed purchased. 
Soiling crops are to be provided ; corn silage and clover are the 
main coarse fodders. 

CONSERVATION OF FERTILITY 

342. Manures Necessary for Conservation of Fertility. 

— In order to conserve the fertility of the soil, not only 
must a systematic rotation be practiced, but a proper 
use must be made of the crops produced. When crops 
are sold from the farm and no restoration is made, soils 
are gradually depleted of their fertility. No soil has 
ever been found that will continue to produce crops 
without the use of manures. Many prairie soils give 
large yields for long periods without manuring, but 
they are never able to compete in productiveness with 
similar soils that have been systematically cropped and 
manured. With a fertile soil the decline in fertihty is 
so gradual that it is not observed unless careful records 
are kept of the yields from year to year. 

j 

j 343. Use of Crops. — The use made of crops whether 

las food for stock or sold directly from the farm de- 
termines the future crop-producing power of the soil. 
jWith different systems of farming different uses are 
|made of crops. When exclusive grain farming is fol- 
liowed there is no restoration of fertility, while in the 
Ipase of stock farming, the manure produced contains 
Jiertility in proportion to the food consumed. If good 



286 SOILS AND FERTILIZERS 

care is taken of the manure, and in place of the grains 
sold mill products are purchased and fed, there is no 
loss but often a gain of fertility. Between these two 
extremes, exclusive grain farming and stock farming, 
many different systems are practiced which remove 
from the soil various amounts of fertility. 

344. Two Systems of Farming Compared. — Losses 
of fertihty from farms are determined by the products 
sold, the care of the manure, and the fertility in the 
materials purchased and used on the farm. If an ac- 
count were kept of the income and outgo of the fertility 
it would be found that with some systems the soil 
is gaining, while with others a rapid decline is occur- ' 
ring. In studying the income and outgo of fertility, it 
is necessary to calculate the amounts of the three prin- 
cipal elements, nitrogen, phosphoric acid, and potash in 
the crops and other products sold. For making these I 
calculations, tables are given in Sections 185 and 307. 
In the handling of manure it is impossible to prevent 
losses, but it is possible to reduce them to very small 
amounts. Hence in the calculations, a loss of 3 per 
cent is allowed for mechanical waste and for uneven 
distribution of the manure ; that is, in addition to the , 
fertility sold from the farm a mechanical loss of 3 per 
cent is allowed for all crops raised and consumed as 
food by stock. 

On one farm the crops raised and sold are : flax 40 
acres, wheat 50 acres, oats 20 acres, barley 50 acres. 



CONSERVATION OF FERTILITY 



287 



No stock is kept, the straw is burned, and the ashes 
are wasted. In addition to the nitrogen removed in 
the crops other losses must be considered. Experiments 
show that when exclusive grain farming is practiced, 
for every pound of nitrogen removed in the crop, 4 
pounds are lost from the soil in other ways. This would 
make the total loss of nitrogen over 28,500 pounds, 
or 177 pounds per acre, which large as it may seem 
is the actual loss from the soil when grain only is raised 
and it is sold. Experiments at the Minnesota Experi- 
ment Station with a soil that had been cultivated 40 
years, showed the annual loss per acre of nitrogen in 
exclusive wheat raising to be 25 pounds through the 
crop and 146 pounds due to oxidation of the nitroge- 
nous humus of the soil.^ 

Exclusive Grain Farming 
Sold from the Farm 



Potash 
Pounds 



Flax, 40 acres . 
Flax straw . 
Wheat, 50 acres 
Wheat straw 
Oats, 20 acres . 
Oat straw 
Barley, 50 acres 
Barley straw 
Total . . 



Nitrogen 
Pounds 


Phosphoric 

Acid 

Pounds 


1600 


600 


600 


120 


1250 


625 


500 


375 


700 


240 


300 


120 


1400 
600 


750 
250 


6950 


3080 



800 

320 

350 

1400 
200 
700 
400 

1500 



5670 



When exclusive grain farming was followed, the annual 
losses of fertility from this farm of 160 acres were 28,5(X> 



288 



SOILS AND FERTILIZERS 



pounds of nitrogen, 3000 pounds of phosphoric acid, 
and 5500 pounds of potash. 

On a similar farm of 160 acres the crops are rotated 
as described in Section 341. The amounts of fertility 
in the crops raised and consumed as fodder, in the 
products sold, and in the food and fuel purchased, are 
given in the following table : 

Stock Farming 
Sold from the Farm 



Butter, 5000 pounds . . . 
Young cattle, 10 head . . 
Hogs, 20 of 250 pounds each 

Steers, 2 

Wheat, 10 acres .... 

Flax, 10 acres 

Rye, ID acres 

Total 



Nitrogen 
Pounds 



5 

200 

100 

48 

250 

390 
285 

1278 



Phosphoric 

Acid 

Pounds 



5 
190 
40 
38 
125 
150 
128 
676 



Potash 
Pounds 



5 

16 
10 

4 

70 

190 

ll 
380 



Raised and Consumed on the Farm 



Clover, 20 tons 

Timothy, 20 tons 

Corn, 20 acres 

Corn fodder, i acre 

Mangels, 2 acres 

Potatoes, I acre 

Straw, 40 tons 

Peas, 5 acres 

Oats, 20 acres 

Barley, 20 acres with straw . . 

Total 

Mechanical loss of food consumed, 
3 per cent 




CONSERVATION OF FERTILITY 



289 



Food and Fuel Purchased 



Bran, 5 tons 

Shorts, 5 tons 

Oil meal, i ton 

Hard wood ashes 

Total 

Mechanical loss of material pur- 
chased, 3 per cent 

Sold from farm 

Loss of food consumed, etc. . . 
Total 

Food and fuel purchased . . . 
Balance lost from farm . . . . 



Nitrogen 
Pounds 



275 
250 
100 

625 



19 

1278 

128 

1425 

625 
800 



Phosphoric 

Acid 

Pounds 



260 

150 

35 

470 



14 
676 

743 

470 
273 



Potash 
Pounds 



150 
100 

25 
100 

375 



10 
380 
144 
534 

375 
159 



The manure produced and used on this farm results 
in larger crop yields than is the case with exclusive grain 
culture. The nitrogen gained by the clover and peas 
more than balances the loss of nitrogen in other crops. 
Experiments show that a rotation similar to this caused 
an increase in soil nitrogen. ^^ Manure, meadow, and 
pasture all tend to increase the soil's humus and ni- 
trogen. The losses of phosphoric acid and potash 
are very small, averaging about a pound per acre of 
each. The manure on this farm is continually bringing 
into activity the inert plant food of the soil so that 
every year there is a larger amount of more active 
plant food, which results in producing larger yields 
per acre. 



290 SOILS AND FERTILIZERS 

The method of farming has a marked effect upon 
crop yields. The average yield of wheat in those 
counties in Minnesota where live stock is kept and 
crops are rotated, is over 10 bushels per acre greater 
than in similar counties where exclusive grain farming 
is followed. 

Problems 

Calculate the income and outgo of fertility from the following 
farms : 

1. Sold from the farm: wheat 40 acres, oats 40 acres, barley 40 
acres, rye 20 acres, flax 10 acres. The straw is burned and no 
manures are used. 

2. Sold from the farm : wheat 20 acres, barley 20 acres, flax 5 
acres, 1000 pounds of butter, 10 hogs, and 10 steers. Purchased : 
bran 3 tons, shorts 2 tons, oil meal i ton. Crops produced and fed 
on farm : clover and timothy hay 40 tons, corn fodder 3 acres, 
corn 10 acres, oats and peas 10 acres, roots i aae, millet i acre, 
and barley 5 acres. 

3. Sold from the farm : wheat 10 acres, sugar beets 5 acres, milk 
100,000 pounds, butter 500 pounds, 20 pigs, 6 head of young stock, 
2 acres of potatoes. Purchased : 5 tons of bran, 2 tons of oil meal, 
I ton of cottonseed meal, 15 cords of wood, i ton of acid phosphate, 
1000 pounds of potassium sulphate, and 500 pounds of sodium |j 
nitrate. Raised and consumed on the farm : corn fodder 15 acres, 
mangels i acre, peas and oats 5 acres, clover 20 tons, timothy 10 
tons, straw from grain sold, oats 10 acres, corn 20 acres. 

4. Calculate the income and outgo of fertility from your owa 
farm. 



CHAPTER XIII 
PREPARATION OF SOILS FOR CROPS 

345. Importance of Good Physical Condition of Seed 
Bed. — But few soils are in suitable condition for seed- 
ing without further preparation than simply plowing the 
land. If the plowing is poorly done, a good seed bed 
cannot be made. The depth of plowing is of prime 
importance and is determined largely by the ■ kind of 
soil, as sand, clay, or loam. (See Section 35.) The 
condition of the seed bed is influenced not only by the 
depth of plowing but by its nature as the way in which 
the furrow slice is left. The treatment after plowing, as 
disking, harrowing, cultivating, and light rolling, must be 
determined largely by the character of the soil. Too 
frequently the preparation of the soil is not given suf- 

I ficient attention and the crop suffers because of a poorly 
prepared seed bed. Low yields are more generally due 

1 to poor physical condition of the soil than to any other 

I factor. Without the requisite cultivation the natural 
fertility is not used to the best advantage. 

i 

346. Influence of Methods of Plowing upon the Condition 

] of the Seed Bed. — ■ A poor seed bed is sometimes due to 
, complete inversion of the furrow slice and the soil not 
I being sufficiently pulverized. If a heavy sod has simply 
I • 291 



292 



SOILS AND FERTILIZERS 



been inverted, subsequent harrowing and cultivation fail 
to pulverize and loosen the tough sod in the lower part 
of the furrow slice. A good seed bed cannot be made 
upon such a foundation. When the land is plowed so 
the furrow slice is left at an angle of 30° to 45°, the sur- 




FlG. 47. Complete Inversion of the Furrow Slice (after Roberts). A poor way 
of plowing sod land. 

face is corrugated and all vegetation is buried in loose 
soil. When land that has been plowed in this way is 
cultivated and harrowed, a better seed bed is formed 
than is possible on a completely inverted furrow slice. 

The plowing should thoroughly pulverize the soil, 
completely bury all surface vegetation, and leave the 
land in a corrugated condition with the furrow slice at 



PREPARATION OF SOILS FOR CROPS 



293 



an angle but firmly connected with the subsoil. There 
should be as thorough disintegration of the soil as pos- 
sible, and this can best be accomplished by the use of 
a plow with a bold rather than too flat a moldboard. 










•^-v^ 



Fig 48. The Furrows standing nearly edgewise (after Roberts). A good 
way to leave tail plowed land to undergo weathering during the winter, to 
be followed by thorough cultivation in the spring. 

Roberts states that only about 10 per cent of the energy 
required for plowing is used by the friction of the mold- 
board : "about 35 per cent of the power necessary to 
plow is used by the friction due to the weight of the 
plow, and 55 per cent by severing the furrow slice and 
the friction of the land slide." Hence in the prepara- 
tion of the seed bed, it is economy to secure as much 
pulverization of the soil by the action of the plow as 
possible rather than to leave too much for subsequent 
treatment. The plow is the most economical implement 
for pulverizing the land. 



294 



SOILS AND FERTILIZERS 



347. Influence of Moisture Content of the Soil at the 
Time of Plowing. — The condition of the soil, particu- 
larly its moisture content, at the time of plowing, has 
much to do with the formation of a good seed bed. If 
soils are too dry when plowed, they fail to pulverize, and 







Fig. 49. Ideal Plowing (after Roberts) . The land left in a formed, pulverized 
condition and all the sods turned under. 

then disking, harrowing, and in some cases light rolling, 
which make additional expense, must be resorted to 
in order to produce a fine, mediumly compact, and well- 
pulverized seed bed. If clay soils are plowed when too 
wet, the pores of the subsoil become clogged, a condi- 
tion known as puddling takes place, and the furrow 
slice dries and forms hard lumps and clods. The con- 
dition in which the soil is left after plowing, particularly 
in the case of clay soils, has much to do with the char- i 
acter of the seed bed and the subsequent yield of the 
crop. At the Oklahoma Station, winter wheat land 
plowed in July was moist and mellow, while that plowed 






PREPARATION OF SOILS FOR CROPS 295 

in September was dry and lumpy ; the early plowed 
mellow land gave a yield of 31.3 bushels per acre and 
the late plowed lumpy land produced only 13.3 bushels. 

348. Influence upon the Seed Bed of Pulverizing and 
Fining the Soil. — If the land is lumpy and the lower 
stratum of the seed bed is not pulverized and firmed, the 
soil water is readily lost by percolation, evaporation takes 
place rapidly, and the crops are poorly fed because the 
roots are unable to penetrate the hard lumps and secure 
plant food. If a soil is inclined to be lumpy, the cul- 
tivation, including the plowing, should be carried on 
largely with the view of thorough pulverization. When 
a seed bed is well prepared, the soil warms up more 
readily ; the loosening and pulverizing enable the 
heat of the sun's rays to more readily penetrate the 
soil and bring it into good condition for promoting 
growth. 

349. Aeration of Seed Bed Necessary. — Crop roots 
require air for functional purposes. In sand and loam 
the air spaces make up half or more of the total 
volume. It is not necessary to cultivate such soil with 
the view of increasing the air spaces, but with compact 
soils, as heavy clays, plowing should result in aeration 
of the soil and an increase in the number of air spaces, 
as the air of the soil takes an important part in render- 
ing plant food available. (See Section 59.) If soils are 
plowed when too wet, they are not sufficiently aerated. 



296 SOILS AND FERTILIZERS 

The amount and kind of cultivation to secure the venti- 
lation or aeration necessary for crop production must 
be regulated according to the character of the soil, as 
sand, clay, or loam, and the climatic conditions. The 
cultivation which is given soils for moisture conserva- 
tion also secures the proper aeration. 

In discussing the importance of a mellow seed bed, 
King says ; ^^ " When a mellow, open seed bed has been 
prepared, and its temperature has been raised to the 
proper point, should a rain fall upon it, that water will 
tend to pass through its wide pores quickly to the 
deeper soil, and without leaching it as badly as would 
be the case were the soil more compact ; so that in 
the early season when there is an overabundance of 
moisture, it is best, for warmth, for aeration, and to 
lessen loss of fertility by percolation, to have a mellow 
seed bed." 

350. Preparation of Seed Bed without Plowing. — 

Loam soils which have been subjected to a systematic 
rotation of crops ending with corn, need not be plowed, 
but the seed bed for the succeeding grain crop can 
be prepared simply by disking the corn land. Surface 
tillage of the corn crop has sufficiently loosened and 
aerated the soil and has caused an accumulation of 1 
available plant food near the surface which would be 
buried and be less available to the crop if the land were 
plowed too deeply. On heavy clay lands this method 
of preparing the seed bed is not advisable ; but on the J 



PREPARATION OF SOILS FOR CROPS 29/ 

silt soils of the Northwest it has given excellent results 
and is beneficial in promoting crop growth. 

351. Mixing of Subsoil with Seed Bed. — Some soils 
are improved by deep plowing and mixing the surface 
and subsoils to form the seed bed. Such soils are 
usually acid in character and contain a large amount 
of organic matter, in which case the mixing of the 
surface and subsoils improves both the physical and 
chemical properties. With sandy soils the mixing of 
the surface soil with the subsoil is not advantageous, as 
it dilutes the stores of plant food which are greater in 
the surface soil ; then, too, the physical properties of 
the soil are not improved. Combining the surface and 
subsoils in the case of heavy clays should be done 
gradually and at each period in the rotation after an 
application of farm manure. In the cultivation of clay 
soils it should be the aim to secure a deep layer of 
i thoroughly pulverized, aerated, and fertilized soil. In 
j the preparation of the seed bed, the character and con- 
dition of the subsoil is equally as important as of the 
j surface soil. 

I 352. Cultivation to Destroy Weeds. — One of the chief 
( objects of cultivation is to destroy weeds, and for this 
purpose it should be given early in the year before 
the weeds become firmly estabhshed. Weeds are most 
I easily destroyed at the time of germination and before 
; the leaves appear above ground. The plow should be 



298 SOILS AND FERTILIZERS 

relied upon largely for the destruction of deep-rooted 
perennial weeds, while the cultivator is effectual for 
the destruction of annuals. When weeds are plowed 
under or destroyed by cultivation they serve as a green 
manurial crop, adding vegetable matter and humus to 
the soil and thus improving its condition instead of 
reducing the yield of crops by appropriating fertility, 
as they do if allowed to grow and mature. Cultivation 
which secures aeration of the soil and conservation of 
the soil moisture is also effectual for the destruction 
of weeds. 

353. Influence of Cultivation upon Bacterial Action. — 
Cultivation has a marked influence upon bacterial ac- 
tion. Some of the soil organisms, as the nitrifying 
organisms (see Section 150), require oxygen for their 
existence, hence cultivation which increases the sup- 
ply of oxygen in the soil increases the activity of such 
organisms. In the absence of air, anaerobic fermenta- 
tion occurs, and such fermentation is unfavorable to 
crop growth. When acid peaty soils are aerated bac- 
terial action is induced which results in more rapid 
decay and a lowering of the per cent of total organic 
matter, including the deleterious organic acids. Neu- 
tralizing the organic acids of soils by applications of 
lime and wood ashes hastens bacterial action, and during 
the process of nitrification this is not alone confined 
to the nitrogenous compounds of the soil, as the nitri- 
fying organisms require phosphates as food and these 



PREPARATION OF SOILS FOR CROPS 299 

are left after nitrification in a more available condition. 
The mineral as well as the organic matter of the soil 
is subject to the action of micro-organisms, and the 
cultivation which the soil receives can be made either 
to accelerate or to retard this action. Many of the 
chemical changes which take place in the soil result- 
ing in the liberation of plant food are induced by aerobic 
organisms, hence the importance of thorough cultiva- 
tion to induce bacterial action. Each type of soil has 
its own characteristic microscopic flora, which can be 
either favorably or unfavorably influenced by cultivation. 

354. Cultivation for Special Crops. — While the gen- 
eral principles of cultivation apply to all crops, the ex- 
tent to which loosening or compacting should be carried 
must be determined by the character of the soil and the 
crop that is to be produced. Methods of cultivation 
must be varied to meet the requirements of different 
soils and different crops. The physical condition of 
the soil for general farm crops is discussed in Chapters 
I and XL For the production of a special crop, the 
cultivation must be adapted to the specific needs as 
to manner of growth, kind of food needed, physical 
condition of the soil, temperature, and moisture. A 
knowledge of these requirements can be obtained only 
by experimental methods. The cultivation of a new 
crop should not be attempted on a large scale without 
a preHminary study of the crop. The production of 
sugar beets for the manufacture of sugar, of flax for 



300 SOILS AND FERTILIZERS 

fine fiber, or of tobacco under shade requires a high 
degree of both knowledge and skill. For the pro- 
duction of special crops the preparation of the seed 
bed and the subsequent cultivation are matters of prime 
importance, and should receive careful consideration on 
the part of the cultivator. Many times agricultural 
industries undertaken in new countries have failed 
because the cultivation of the special crop used in the 
industry has not been successfully accomplished on 
account of lack of knowledge of the cultural methods 
necessary. 

355. Cultivation to prevent Washing and Gullying of 
Lands. — In regions of heavy rainfall, rolling land of 
clay texture often becomes gullied by the watpr flowing 
in large amounts over the surface. Under such condi- 
tions the preparation of a seed bed, and cultivation of 
the soil so as to prevent washing are often difficult prob- 
lems. To prevent gullying, the water currents should 
be divided as much as possible by plowing narrower 
lands and by increasing the number of shallow dead 
furrows. The larger drains should be constructed with 
the view of preventing the formation of deep guUies, and 
this can in part be accomplished by encouraging the 
growth of special grasses with fibrous roots which serve 
as soil binders. Soils which gully are improved by the 
addition of farm manures and other humus-forming 
material which bind together the soil particles ; also by 
seeding and cultivating at right angles to the slope of 



PREPARATION OF SOILS FOR CROPS 3OI 

the land so as to break the force of the water. The 
water should be encouraged to percolate through the 
soil rather than to flow over the surface. (See Section 
25.) 

356. Bacterial Diseases of Soils. — Many of the bac- 
terial diseases to which crops are subject are caused 
primarily by a diseased condition of the soil. These 
diseases can often be checked by the right kind of culti- 
vation, by securing good drainage, and by proper soil 
ventilation supplemented with the application of alkaline 
, matter as wood ashes and land plaster. Undrained soils 
I are unsanitary ; the products of decay of the organic 
' matter accumulate in the soil and produce toxic or poi- 
(sonous compounds which affect crops. When soils are 
,1 drained, air is admitted which prevents the formation 
iof these products. Both bacterial and fungous diseases 
(of soils may be controlled by cultivation, particularly 
when it improves the general sanitary condition of the 
iSoil. With improvement in sanitary condition, there 
:|is less liability of bacterial diseases becoming established 
land causing destruction of the crop. As a result of 
jSome forms of bacterial action, chemical substances in- 
jjurious to plants are produced, and by controlling bac- 
iterial action the formation of these is prevented. Some 
of the organisms propagated in the soil cause bacterial 
|diseases of dairy and other farm products. The use of 
isoil disinfectants is possible only where a small area is 
ijinvolved ; they are not applicable to large tracts as they 



302 SOILS AND FERTILIZERS 

destroy the beneficial as well as the injurious soil 
organisms. A good sanitary condition of the soil is 
as essential for the production of crops as are suitable 
hygienic surroundings for the rearing of live stock. 
Sunlight and air are important factors in bringing about 
an improved sanitary condition of diseased soils. 

By the rotation of crops many bacterial diseases, as 
flax wilt and clover sickness, are controlled. Some of 
these are disseminated by the use of infected seed. 
By sprinkling the seed grain with a disinfectant as a 
dilute solution of formalin (i pound of formalin in 50 
gallons of water) bacterial diseases, as grain smuts, ; 
are held in check. Low forms of plants, as fungi, 
also develop in soils when conditions are favorable, \ 
and take an important part in changing the char-; 
acter of the soil. Their action may be either beneficial I 
or injurious, depending upon the condition of the soil 
There is a very close relationship between soil san- 
itation, which results in the avoidance of crop diseases, 
and the quality and yield of agricultural products. 

357. Influence of Crowding Plants in the Seed Bed. — j 

The number of plants which a seed bed should produce 
is dependent mainly upon the supply of water and plant 
food. By means of thick or thin seeding, the general 
character of crops may be influenced within definitei 
limits. Either an excessive or a scant amount of seedj 
gives poor results. If overcrowded, plants fail to de- 
velop normally either for want of plant food or water, or 



PREPARATION OF SOILS FOR CROPS 303 

because of poor sanitary conditions, or from lack of 
room for development. Experiments show that an ex- 
cessive amount of seed wheat as more than lOO pounds 
per acre of spring wheat does not give good results. 
Each crop has its limit beyond which it is not desirable 
to crowd the plants in the seed bed. When there is 
crowding, unhygienic conditions prevail and the lack of 
air, sunhght, and good ventilation encourages bacterial 
diseases, while on the other hand too few plants favor 
the growth of weeds and an abnormal development of 
the crop. In the seeding of grains and other farm crops, 
the amount of seed to be used per acre should be deter- 
mined by the quality of the seed and the local conditions, 
as climate and soil, together with any special character- 
istic desired in the way of composition and character of 

the crop. 

I 

358. Selection of Crops. — The selection of the most 
suitable crops to be grown is largely a local problem and 
must be determined by climatic and soil conditions. The 
preference of farm crops for certain types of soil is dis- 
cussed in Sections ii to 17, and it is not advisable to 
attempt to grow crops upon soils to which they are not 
naturally adapted or under unfavorable climatic condi- 
tions. Practical experience is the best guide in re- 
gard to the selection of crops and the most suitable 
lines of farming to follow, and it will be found that this 
experience is in harmony with the laws governing the 
conservation and development of the fertility of the soil. 



304 SOILS AND FERTILIZERS 

Temporary methods of farming, as exclusive grain raising, 
can be foilowed for a short time on new soils ; but it is 
desirable that each type of soil should be subjected to a 
judicious system of cultivation, fertilizing, and cropping 
rather than to the production of one or only a few mar- 
ket crops at random. The selection of the crops and 
their utilization for market or feeding purposes should 
be determined mainly by the system of farming that is 
most adapted to the soil of the farm, and the farm 
should be managed largely with the view of maintain- 
ing the fertility of the soil. 

359. The Inherent and Cumulative Fertility of Soils. ^^ 
— There is present in nearly every soil a variable 
amount of inherent fertility resulting from disintegration 
and other changes to which soils are subject. In some 
long-cultivated soils the amount of fertility produced 
annually by weathering and natural agencies is sufficient 
to yield from ten to fifteen bushels of wheat per acre. 
This does not represent the maximum crop-producing 
power of the soil, but simply the inherent or natural fer- 
tility. When the natural fertility is reenforced with farm 
manures and other fertilizers, culmulative fertility is 
added and maximum yields are secured. In many soils 
there are large amounts of cumulative fertility or resi- 
dues from former applications of manure. The crop- 
producing power of a soil is dependent upon both the 
inherent and the cumulative fertility, as well as upon 
the mechanical condition of the soil. In the production 



PREPARATION OF SOILS FOR CROPS 305 

of crops, all of the inherent fertility should be utilized to 
the best advantage, and cumulative fertility should be 
added so that the stock of total fertility may be increased. 
Soils of the highest fertility are those which are com- 
posed of a large amount of silt or particles of equivalent 
value, well drained, but sufficiently retentive of mois- 
ture for crop production, and of good capillarity. Such 
soils are usually deposited by water ; they are uniform 
in texture, of great depth, and contain large amounts of 
organic matter rich in nitrogen and minerals contain- 
ing all of the essential elements of plant food. When 
these soils are cultivated, the organic matter readily 
undergoes decay with liberation of plant food. 

360. Balanced Soil Conditions. — A high state of 
fertility necessitates a balanced condition of the phys- 
ical and chemical properties of a soil. Some soils are 
of good texture and have all the necessary physical 
requisites for crop production, but fail to produce good 
crops because of a scant supply of the essential elements 
of plant food. Other soils contain the necessary plant 
food but are unproductive because of poor physical 
condition. Soils may be unproductive on account of 
either chemical or physical defects, causing the various 
factors of soil fertility to be unbalanced. In the cul- 
tivation of a soil it should be the aim to discover any 
defect and then to apply the necessary corrective 
measures. Soil problems are extremely varied in char- 
acter, and the cultivator of the soil should seek aid jointly 

X 



306 SOILS AND FERTILIZERS 

from chemistry, physics, biology, and geology, and also 
from practical experience founded upon observation in 
the cultivation of soils and the production of crops. 
The utilization and maintenance of the fertility of the 
soil of necessity form the basis of any rational agricul- 
tural system. 



CHAPTER XIV 

LABORATORY PRACTICE 

The laboratory practice is an essential part of the work in Soils 
and Fertilizers, as the experiments illustrate many of the funda- 
mental principles of the subject. The student should endeavor to 
cultivate his powers of observation so as to grasp the principles in- 
volved in the work rather than to do it in a merely mechanical or 
perfunctory way. Neatness is one of the essentials for success in 
laboratory practice ; an experiment performed in a slovenly manner 
is of but little value. 

A careful and systematic record of the laboratory work should be 
kept by the student in a suitable note-book. In recording the re- 
sults of an experiment, the student should give in a clear and con- 
cise form the following : 

(i) Title of the experiment. 

(2) How the experiment is performed. 

(3) What was observed. 

(4) What the experiment proves. 

The note-book should be a complete record of the student's in- 
dividual work, and should be written up at the time the experiment 
is performed. 

Before an experiment is made the student is advised to review 
those topics presented in the text which have a bearing upon the 
experiment, so a clearer conception may be gained of the relation- 
ship between the laboratory work and that of the class room. 

Students who have had but little laboratory practice are advised 
to study the chapters on Laboratory Manipulation, and Water and 
Dry Matter, in "The Chemistry of Plant and Animal Life." 

307 



3o8 



SOILS AND FERTILIZERS 



Some of the pieces of apparatus are loaned to the student when 
needed to perform the experiment ; for these a receipt is taken, and 
he is credited with the apparatus when it is returned. 

The following are supplied to each student : — 



I Crucible Tongs. 

I Pkg. Filter Paper. 

I Test Tube Clamp. 

I Evaporator. 

I Stirring Rod. 

3 Beakers. 

6 Test Tubes. 

I Test Tube Stand. 

I Funnel. 

I Mortar and Pestle. 



No. 



I 


2 Bottles. 


No 


II 


2 


I Large Cjlinder. 




12 


3 


I Sand Bath. 




13 


4 


I Hessian Crucible 




14 


5 


I Wooden Stand. 




15 


6 


I Tripod 




i6 


7 


I Ring Stand and 


3 Rings- 


17 


8 


I Single Clamp. 




i8 


9 


I Burner and 2 Ft. 


Rubber 







Tubing. 




»9 




I Brush. 




20 



Directions for Weighing. — Place the dish or material to be 
weighed in the left hand pan of the balance. (See Fig. 51.) With 
the forceps lay a weight from the weight box on the right hand pan. 
Do not touch the weights with the hands. If the weight selected is 
too heavy, replace it with a lighter weight. Add weights until the 
pans are counterpoised ; this will be indicated by the needle swing- 
ing nearly as many divisions on one side of the scale as on the other. 
The brass weights are the gram weights. The other weights are 
fractions of a gram. The 500, 200, 100 mg. (milligram) weights are 
recorded as .5, .2, and .1 gm. The 50, 20, and 10 mg. weights 
as 0.05, 0.02, and o.oi gm. If the 10, and 2 gm. and the 200, the 
100, and the 50 gm. weights are used, the resulting weight is 
12.35 gnis. No moist substance should ever come in contact with 
the scale pans. The weights and forceps should always be replaced 
in the weight box. Too much care and neatness cannot be exer- 
cised in weighing. 

General Direction for Laboratory Practice. — The student should 
write up the results of his experiments at the time they are per- 



LABORATORY PRACTICE 



509 



formed. Careful attention should be given to the spelling, language, 
and punctuation, and the note-book should represent the student's in- 
dividual work. He who attempts to cheat in laboratory work by 
copying the results of others only cheats himself. Care should be 
exercised to prevent anything getting into the sinks that will clog 




Fig. 51. Balance and Weights. 

the plumbing; soil, matches, broken glass, and paper should be de- 
posited in the waste jars. The student should learn to use his 
time in the laboratory profitably and economically. He should ob- 
tain a clear idea of what he is to do, and then do it to the best of 
his ability. If the experiment is not a success, repeat it. While 
the work is in progress it should be given undivided attention. 



3IO 



SOILS AND FERTILIZERS 



Experiment No. i 
Determination of the Hydroscopic Moisture and Volatile Matter of 

Soils 




Fig. 52. Apparatus for determining Moisture Content of Soils. 

Weigh in grams to the second decimal place a dry Hessian 
crucible. Place 5 to 10 gms. of air-dried soil in the crucible 



LABORATORY PRACTICE 



311 



and weigh again. Then place the dish containing the soil in the 
water oven and leave it four hours for the soil to dry. Cool and 
weigh at once so there may be as 
little absorption of water from the 
air as possible. From the loss of 
weight, calculate the per cent of 
hydroscopic moisture in the soil. 
Place the crucible containing the 
dry soil in a muffle furnace and 
leave until all of the organic mat- 
ter is volatilized. After the cru- 
cible has cooled on an asbestos 
mat, weigh and calculate the per 
cent of volatile matter. The vola- 
tile matter consists of organic mat- 
ter and water that is held in chemi- 
cal combination with the silicates. 
(Soils from the students' home 
farms are to be used in Experi- 
ments Nos. I, 2, 4, 6, 9, 12, 16, 18, 
19, and 21, each student working 

with his own soil.) Fig. 53. Muffle Furnace used for de- 

termining Volatile Matter. 




Experiment No. 2 

Determination of the Capacity of Loose Soils to absorb Water 

To 100 gms. of air-dried soil in a beaker add 100 cc. of water. 
Mix the soil and water, then pour the mixture on a saturated 
but not dripping filter paper fitted into a funnel. For transfer- 
ring the soil, 50 cc. more water may be used. Measure the drain 
water in a graduate. To prevent evaporation, keep the moist soil 
in the funnel covered with a glass plate. Deduct the leachings 
from the total water used. Calculate the per cent of water retained 
by the air-dried soil. 



312 



SOILS AND FERTILIZERS 



Repeat the experiment, using sand, and note the difference in 
absorptive power. 

Repeat, using 95 per cent of sand and 5 per cent of dry and 
finely pulverized manure. 



Experiment No. 3 
Determination of the Capillary Water of Soils 

For this experiment a sample of soil directly from the field is 

to be used. The .sample is to be 
taken at a depth of from 3 to 9 
inches or at any depth desired. 
One hundred grams of soil are 
weighed into a tared drying pan, 
exposed in a thin layer to the room 
temperature for 24 hours and then 
reweighed. After an interval of 
from two to four hours the soil is 
weighed again, and if the weight is 
fairly constant, the per cent of water 
lost by air drying, representing the 
capillary water of the soil at the time 
of sampling, is calculated. This ex- 
periment may be repeated, using 
different types of soil, as sand, clay, 
and loam. 



Experiment No. 4 

Capillaiy Action of Water upon 
Soils 

The Capillary Water of firmly tie a piece of linen cloth 

yoiis. over the end of a long glass tube 

4 inches in diameter, then fasten a piece of wire gauze over 
the cloth. Fill the tube with sandy soil (No. I). Compact the soil 




Fig. 54. 



LABORATORY PRACTICE 313 

after the addition of each measured quantity by allowing the weight 
from the compaction machine (see Experiment No. 8) to drop twice 
from the 12-inch mark. 

In a similar way, fill a second and a third tube with clay 
and loam respectively ; immerse the lower ends of the tubes in 
a cylinder of water and support the tubes, as shown in the illus- 
tration. Measure each day for one week the height to which the 
water rises in the soils. If desired, three more tubes filled loosely 
with the soils may be added, and the influence of compaction 
upon the capillary rise of water in the soils noted. 

Experiment No. 5 

Influence of Manure and Shallow Surface Cultivation upon the 
Moisture Content and Temperature of Soils 

Weigh and fill four boxes, each a foot square and a foot deep, 
as follows : one with air-dried sand, one with clay, one with loam, and 
one with sand containing 5 per cent of fine dry manure. Deter- 
mine the hydroscopic moisture of each sample. Weigh the boxes 
after adding the soils which should be moderately compacted. To 
each add the same amount of water slowly from a sprinkling pot, 
carefully measuring the water used. The soil should be well mois- 
tened, but not supersaturated. Each box is to receive shallow sur- 
face cultivation, using for the purpose a gardener's small tool. Leave 
the boxes exposed to the sun or in a moderately warm room. At the 
end of one or two days take a sample of soil from the center of 
each box at a depth of 4 to 8 inches and determine the moisture 
content as directed in Experiment No. i. Note the differences in 
moisture content. Weigh the boxes. Take the temperature of the 
soil in each box. 

Experiment No. 6 
Weight of Soils 

Determine the cubic contents of a box about 4 inches square. 
Weigh the box. Determine its weight when filled, not compacted, 



314 



SOILS AND FERTILIZERS 



■with air-dry sand, with clay, with loam, and with peaty soil. Com- 
pute the weight per cubic foot of each soil. Calculate the weight 

of water held by the 
box. Determine the ap- 
parent specific gravity. 

Experiment No. 7 
Influence of Color upon 
the Temperature of 
Soils 

Expose to the sun's 
rays, dry clay, dry sand, 
and moist and dry peat. 
After two hours' expo- 
sure take the tempera- 
ture of each. The bulb 
of the thermometer 
should be just covered 
with the soil. All of 




l-'ii^. 55- 



Determining the Weight per Cubic Foot 
of Soils. 



the observations should be made under uniform conditions. 



Experiment No. 8 

Movement of Air through Soils 

Fill, without compacting, a soil tube 12 inches high and 3 inches 
in diameter with sifted loam soil. Nearly fill the outer cylinder with 
water, open the stopcock, and allow the inner cylinder to sink in 
the water, close the stopcock and connect the aspirator to the soil tube 
with a rubber tube. Adjust the weight, 2, open the stopcock, and 
note the time required for 5 liters of air to aspirate through the soil. 
-In like manner fill tubes with sand, gravel, peat, and clay, and deter- 
mine the time required for 5 liters of air to be aspirated through 
each. In filling the tubes, care should be taken that all are treated 
alike. Repeat the experiment, using soil from your own farm loosely 



LABORATORY PRACTICE 



315 



filling one tube, and moderately compacting another with the com- 
pacting machine. Note the difference in time required for the air 
to pass through the loose and the compacted soil. 





1[ 

T 


i 





Fig. 56. Aspirator for determining the Rate of Movement of Air through Soils. 
(Adapted from Bui. 107, U. S. Dept. Agr., Office of Expt. Stations.) 



Experiment No. 9 
Separation of Sand, Silt, and Clay 

For this experiment the student should use some of the soil from 
his home farm. Ten grams of air-dried and crushed soil which have 



3i6 



SOILS AND FERTILIZERS 



been passed through a sieve with holes 0.5 mm. in diameter are 
placed in a mortar and about 20 cc. of water added. The soil is 
pestled with a rubber-tipped pestle with the object of separating 
adhering particles without pulverizing the individual soil grains. 
After two or three minutes' pestling, more water is added and the 
soil and water are allowed to sediment for about one minute ; the 
turbid liquid is then decanted into a bealcer. This process of soft 

pestling and decan- 
tation is repeated 
two or three times 
until the remaining 
soil grains appear 
free from adhering 
smaller particles. 
With some .soils 
this is a tedious 
process. The con- 
tents of the mortar 
are then transferred 
to the beaker and 
enough water added 

Fig. 57. The MechanK-al Analysis of So.is. ^^ ^^^^^^ ^jl ^he 

beaker. The contents of the beaker are thoroughly stirred, and after 
two or three minutes' sedimentation, the turbid liquid is decanted 
into a second beaker, leaving the sediment in the first beaker. More 
water is added to the first beaker, and the stirring, sedimentation, 
and decantation are repeated until the sediment consists mainly of 
clean fine sand. After about ten minutes the turbid liquid in the 
second beaker is decanted into a large cylinder, the sediment in the 
beaker being washed with more water and the washings added to the 
cylinder. It is to be noted that the sediment in the second beaker 
is composed of finer particles than the sediment in the first beaker. 
The sediment in the first beaker consists mainly of medium and fine 
sand, and in the second beaker of fine sand and coarse silt. Some 




LABORATORY PRACTICE 



317 



sand particles are carried along in the washings into the large cylinder. 
It is difficult to make even an approximate separation of a soil into 
sand, silt, and clay particles. In the mechanical analysis of soil, the 
chemist uses the microscope 
to determine when the sepa- 
rations are reasonably com- 
plete. The sediment in the 
cylinder consists mainly vi 
silt. The fine particles whicli 
remain suspended in the water 
of the cylinder and cause the 
roiled appearance are mainly 
the clay particles. In this 
experiment note approxi- 
mately what grades of soil 
particles predominate 1h your 
soil. Save the liquid in the 
cylinder for the next experi- 
ment. 

Experiment No. 10 
Sedimentation of Clay 

In each of three separate 
cylinders or beakers place 
200 cc. of the turbid liquid 
saved from Experiment No. 
9. To beaker No. I. add 0.5 
gm. calcium hydroxide and Fig. 58. Movement of Water through Soils, 
stir. To beaker No. 2, add 

I gm. of calcium hydroxide and stir. The third beaker is used for 
purposes of comparison and no calcium hydroxide is added. After 
24 hours examine the three beakers and note the influence of the 
calcium hydroxide in precipitating the clay and clarifying the liquid. 




3l8 SOILS AND FERTILIZERS 

Experiment No. ii 
Deportment of Soils when Wet 

Place about 5 gms. of the soil used in Experiment No. 9 in the 
palm of the hand. Wet and knead. Note whether a plastic mass 
is formed. If the soil is sticky, it indicates the presence of plastic 
clay. Rub some of the soil between thumb and finger ; if it is com- 
posed largely of clay, it will feel smooth and oily. The sand parti- 
cles impart a sharp gritty feeling ; in the presence of clay this is more 
or less modified. Note wliether the lumps of dry soil crush easily. 
The way a soil responds when crushed, wet, and kneaded, gives 
some idea of its tillage properties. 

Experiment No. 12 
Rate of Movement of Water through Soils 

Weigh a soil tube and fill it to within two inches of the top with 
sand. Weigh again. In like manner weigli and fill two other 
tubes, one with clay and one with loam. Support the tubes from 
the ring stand as noted in Fig. No. 58. Place a receptacle under 
the outlet of each tube. Measure into cylinders or large beakers 
three 500 cc. portions of water. From one of these beakers slowly 
pour the water into the sand cylinder, and note the length of time 
required for the water to percolate through the sand, and the amount 
of water that percolates in a given time. Replenish the water in 
the beaker with measured amounts as needed. In like manner test 
the clay and the loam. After the water has ceased dripping from 
the tubes, weigh and calculate the amount retained by the soils. 

Experiment No. 13 

Properties of Rocks from which Many Soils are Derived 

Study the laboratory samples of rocks and fill out the following 
table : — 



LABORATORY PRACTICE 



319 



Rocks 


Comparative 
Hardness 


Color 


General 

Form 


Soluble 
IN HCl 


Feldspar . . . 

Mica 

Quartz .... 
Granite .... 
Hornblende . . . 
Limestone . . 











Experiment No. 14 
Form and Size of Soil Particles 
(Note. Special directions for manipulating the microscope, plac- 
ing the material on the microscopical object slide, and focusing will 
be given by the instructor.) 

Place on a microscopical object slide a small amount of soil ; dis- 
tribute it in a thin layer, and examine with a low-power microscope. 
Observe the form and size of the soil particles, distinguish the vari- 
ous grades of sand, silt, and clay, and make drawings of some of the 
particles. 

Experiment No. 15 

Pulverized Rock Particles 

I Examine with a low-power microscope samples of pulverized 
I mica, feldspar, granite, and limestone. Note any similarity to the 
I soil particles examined in Experiment No. 14. 

i Experiment No. 16 

I Reaction of Soils 

For this experiment use peaty, mildly alkaline, and clay soils. 

j Bring in contact with each soil, after moistening with distilled 

( water, pieces of sensitive red and blue litmus paper. Note any 

j changes in color of the litmus paper and state what the results show. 

I In a similar way test the soil from your own farm. 



320 SOILS AND FERTILIZERS 

Experiment No. 17 
Absorption of Gases by Soils 
Weigh 50 gms. of soil into a wide-mouthed bottle, add 50 cc. of 
water and i cc. of strong ammonia. Note the odor. Cork the 
bottle, shake, and after 24 hours again note the odor. To what is 
the fixation of the ammonia due.-* Is this a physical or a chemical 
change? Define fi.xation. 

Experiment No. 18 
Acid Insoluble Matter of Soils 
Weigh 10 gms. of soil into a beaker, add 100 cc. hydrochloric 
acid (50 cc. strong acid and 50 cc. H2O) ; cover the beaker with a 
watch glass; heat on the sand bath in the hood for two hours, re- 
placing the acid solution in case excessive evaporation takes place. 
Filter, transfer, and wash the residue, using 50 cc. distilled water. 
Note the appearance and quantity of insoluble residue. Of what 
does it consist? What is its value as plant food? How does it 
resemble the original soil and in what ways does it differ? Save 
the filtrate for the next experiment. 

Experiment No. 19 
Acid Soluble Matter of Soils 
Divide the filtrate from the preceding experiment into three 
equal portions, (i) To one portion add ammonia until alkaline. 
The precipitate formed consists of iron and aluminum hydroxide and 
phosphoric acid. Note the color and gelatinous appearance of this 
precipitate. When dried it occupies only a small volume. Filter 
and remove this precipitate which contains lime, magnesia, potasli. 
and soda. To the filtrate add 20 cc. of ammonium oxalate ; warm 
on the sand bath, and note any precipitate of calcium oxalate 
that is formed. (2) Evaporate the second portion nearly to dry- 
ness. Add"20 cc. distilled H^O and 3 cc. HNO3; warm to dissolve 



LABORATORY PRACTICE 321 

any residue. Add 5 to 7 cc. of ammonium molybdate, heat gently, 
and shake. The yellow precipitate is ammonium phosphomolyb- 
date, which contains the element P in mechanical and chemical com- 
bination. (3) Evaporate the third portion in the evaporating dish 
on the sand bath. Of what does the residue consist and what 
elements does it contain? 



9 



Experiment No. 20 
Extraction of Humus from Soils 

Place 10 gms. of soil in a bottle (preferably a glass-stop- 
pered one) and add 200 cc. HgO and 5 cc. HCl. Shake and allow 
10 to 24 hours for the acid to dissolve the lime so the humus 
can be dissolved by the alkali. Filter the acid and wash the soil 
on the filter with distilled water until the washings are no longer 
acid to litmus paper. Transfer the soil to the bottle again, add 
100 cc. HgO and 5 cc. KOH solution. Shake, and after two to 
four hours filter off some of the solution which is dark-colored 
and contains dissolved humus compounds. 

To 10 cc. of the filtered humus solution add HCl until neutral. 
The precipitate formed is mainly humic acid and soil humates. 
Evaporate a second portion of 10 to 20 cc. to dryness ; the black 
residue obtained is humus material extracted from the soil. 

Experiment No. 21 
Nitrogen in Soils 
Mix 5 gms. of soil and an equal bulk of soda lime in a mortar; 
transfer to a strong test tube. Connect the test tube with a deliv- 
ery tube which leads into another test tube containing distilled 
water. Heat cautiously for from 5 to 10 minutes, with the Bunsen 
burner, the test tube containing the soil and soda lime. Test the 
liquid with litmus paper and note the reaction. Soda hme aided 
by heat decomposes the organic matter of the soil and forms COg, 
H2O, and NH3. The nitrogen in the form of ammonia is distilled 

Y 



322 



SOILS AND FERTILIZERS 



and absorbed by the water in the second test tube; the reaction 
is due to the presence of the ammonia. 



Experiment No. 22 

Testing for Nitrates 

Dissolve about 50 milligrams of sodium or potassium nitrate in 

100 cc. H^,0. To 15 cc. 
of this solution add 2 cc. 
of a dilute and clear solu- 
tion of FeSO^, and place 
the test tube in a cylinder. 
Through a long-stemmed 
funnel add 2 or 3 cc. HgSO^. 
Observe the dark brown 
ring that is formed ; H2S0^ 
liberates HNO3 as a free 
acid, which in turn changes 
the iron from the ferrous 
to the ferric state ; the dark 
brown color is due to the 
nitric acid forming interme- 
diate compounds during 
this operation. 




Fig. 59. Testing for Nitrates. 



Experiment No. 23 

Volatilization of Ammonium Salts 

In separate test tubes place about o.i gm. each of ammonium 
carbonate and ammonium sulphate. Apply heat gently to each and 
observe the result. Observe that the ammonium carbonate readily 
volatilizes and some is deposited on the walls of the test tube while 
the ammonium sulphate is much less volatile. In poorly ventilated 
barns, deposits of ammonium carbonate are frequently found. 



J 



i 



LABORATORY PRACTICE 



323 



Add slowly and 



Experiment No. 24 
Testing for Phosphoric Acid 

Dissolve 0.5 gm. bone ash in 15 cc. H2O and 3 to 5 cc. HNO^and 
filter. To the warm filtrate add 5 to 7 cc. ammonium molybdate 
and shake. The yellow precipitate formed is ammonium phospho- 
molybdate. See Experiment No. 19. 

In a test tube heat 0.5 gm. of bone ash with 20 cc. distilled 
H„0; filter. To the warm filtrate add 5 cc. ammonium molyb- 
date and shake. Note the result as compared with that when 
HNO3 was used with the distilled water. What does the result 
show ? 

Experiment No. 25 
Preparation of Acid Phosphate 

Place 100 gms. bone ash in a large lead dish, 
with constant stirring loo gms. commercial 
sulphuric acid, using an iron spatula for the 
purpose. Transfer the mixture to a wooden 
box and allow it to act for about th-ree days. 
Then pulverize and examine. The mixing of 
the acid and phosphate should be done in a 
place where there is a good draft. Test { 
gm. for water soluble phosphates as directed 
in Experiment No. 24. 

Experiment No. 26 

Solubility of Organic Nitrogenous Compounds 
in Pepsin Solution 

Prepare a pepsin solution by dissolving 
5 gms. of commercial pepsin in a liter of 
water, adding i cc. of strong HCl. Place in 
separate beakers 0.5 gm. each of dried blood, 
tankage, and bone ash. Add 200 cc. of pep- 
sin solution to each and place the beakers in a 




Fig. 60. Determining 
Digestibility of Organic 
Nitrogen in Acid Pepsin 
Solution. 



324 SOILS AND FERTILIZERS 

water bath kept at a temperature of about 40° C. Stir occasion- 
ally, and at the end of five hours observe and compare the amounts 
of insoluble matter remaining in the beakers, note also the color 
and appearance of the solution in each beaker. See Section 170. 

Experiment No. 27 

Preparation of Fertilizers 

Mix in a box 200 gms. acid phosphate (saved from Experiment 
No. 25), 50 gms. kainit, and 50 gms. sodium nitrate. Calculate the 
percentage composition of this fertiUzer and its trade value. 

Experiment No. 28 

Testing Ashes 

Test samples of leached and unleached ashes in the way de- 
scribed in Section 256. 

Experiment No. 29 

Extracting Water Soluble Materials from a Commercial Fertilizer 

Dry and weigh a 7 cm. filter paper. Fit it in a funnel, and place 
in it 2 gms. of commercial fertilizer. Pass through the filter, a little 
at a time, a half liter of pure water at about 40° C. (distilled 
water preferred). Transfer the filter paper and contents to a watch 
glass, dry in a water oven, weigh and calculate the per cent of 
material extracted by the water. If the fertilizer is made of such 
materials as acid phosphate, kainit, muriate or sulphate of potash, 
nitrate of soda and sulphate of ammonia, from 60 to 90 per cent 
will dissolve. Inspect the insoluble residue and note if it is 
composed of dried blood, bones, or animal refuse material. Of a 
high-grade complete commercial fertilizer from 40 to 80 per cent 
or more should dissolve in water. 



LABORATORY PRACTICE 325 

Experiment No. 30 

Influence of Continuous Cultivation and Crop Rotation upon the 
Properties of Soils 

For this experiment a soil that has been under continuous culti- 
vation, and also one of similar character from an adjoining field 
where the crops have been rotated and farm manures have been 
applied, should be used. Make the following determinations with 
each soil : — 

Weight per cubic foot. 

Capacity to hold water. 

Note the color of each. 

Experiment No. 31 
Summary of Results of Tests with Home Soil 

Make a tabulation of your results including : 

Hydroscopic moisture as determined in Experiment No. i. 

Volatile matter as determined in Experiment No. i. 

Capacity of the loose soil to absorb water. Experiment No. 2. 

Height of rise of capillary water in tube, Experiment No. 4. 

Weight per cubic foot, Experiment No. 6. 

Prevailing kind of soil particles. Experiment No. 9. 

Deportment of soil when wet and kneaded. Experiment No. 11. 

Reaction of soil. Experiment No. 16. 

Amount of acid soluble matter. Experiment No. 19. 

Amount of lime. Experiment No. 19. 

Amount of humus extractive material, Experiment No. 20. 

Crops most suitable for production upon this soil as indicated by 
physical and chemical tests. 

How does this agree with your experience with the crops raised 
on the soil ? 

Probable deficiencies or weak points as indicated by tests or past 
experience. 

What is the most suitable line of farming to follow with this soil 
in order to conserve its fertility? 



326 SOILS AND FERTILIZERS 

Scheme of Soil Classification 

(Adapted from Bureau of Soils Report, U. S. Dept. Agr.) 

Coarse sand contains more than 20 per cent of coarse sand and 
more than 50 per cent of fine gravel, coarse sand, and medium sand, 
less than 10 per cent of very fine sand, less than 15 per cent of silt, 
less than 10 per cent of clay, and less than 20 per cent of silt and 
clay. 

Medium sand contains less than 10 per cent of fine gravel, more 
than 50 per cent of coarse, medium, and fine sand, less than 10 per 
cent of very fine sand, less than 15 per cent of silt, less than 10 per 
cent of clay, and less than 20 per cent of silt and clay. 

Fine sand contains less than 10 per cent of fine gravel and 
coarse sand, more than 50 per cent of fine and very fine sand, less 
than 15 per cent of silt, less than 10 per cent of clay, and less than 
20 per cent of silt and clay. 

Sandy loam contains more than 20 per cent of fine gravel, coarse 
sand and medium sand, more than 20 per cent and less than 35 
per cent of silt, less than 15 per cent of clay, and less than 50 per 
cent of silt and clay. 

Fine sandy loam contains more than 40 per cent of fine and 
very fine sand and more than 20 per cent and less than 50 per cent 
of silt and clay, usually 10 to 35 per cent of silt and from 5 to 15 
per cent of clay. 

Silt loam contains more than 55 per cent of silt and less than 25 
per cent of clay. 

Loam contains less than 55 per cent of silt and more than 50 
per cent of silt and clay, usually from 15 to 25 per cent of clay. 

Clay loam contains from 25 to 55 per cert of silt, 25 to 35 per 
cent of clay, and more than 60 per cent of silt and clay. 

Clay contains more than 35 per cent of clay. 

Sandy clay contains more than 30 per cent of coarse, medium, 
and fine sand, less than 25 per cent of silt, more than 20 per cent of 
clay, and less than 60 per cent of silt and clay. 

Silt clay contains more than 55 per cent of silt and from 25 to 35 
per cent of clay. 



REVIEW QUESTIONS 

CHAPTER I 

I. From what are soils derived ? 2. What are the physical prop- 
erties of soils ? When do soils differ physically, when chemically ? 
3. Why do soils differ in weight ? Arrange clay, sand, loam, and 
peat in order of weight per cubic foot. 4. When wet, what would 
be the order? 5. What is the absolute and what the apparent 
specific gravity of soils ? What is pore space? 6. Define the terms : 
skeleton, fine earth, fine sand, silt, and clay. 7. What are the 
physical properties of clay ? 8. What are the forms of the soil 
particles ? 9. How do different types of soil vary as to the number 
of particles per gram of soil ? 10. How is a mechanical analysis 
of a soil made ? 11. Why do certain crops thrive best on definite 
types of soil ? 12. What factors must be taken into consideration 
in determining the type to which a soil belongs ? 13. Give the 
mechanical structure of a good potato soil. 14. How does a wheat 
soil differ in mechanical structure from a truck soil? 15. A good 
corn soil is also a type for what other crops ? 16. How much 
water is required to produce an average grain crop, and how do the 
rainfall and the water removed in crops during the growing season 
compare ? 17. In what forms may water be present in soils ? 18. 
What is bottom water and when may it be utilized by crops ? 19. 
What is capillary water ? 20. Explain the capillary movement of 
water. 21. Explain how the capillary and non-capillary spaces in 
the soil may be influenced by cultivation. 22. What is hydroscopic 
water and of what value is it to crops ? 23. What is percolation ? 
24. To what extent may losses occur by percolation ? 25. What 
are the factors which influence evaporation ? 26. What is transpira- 
tion ? 27. In what three ways may water be lost from the soil ? 
28. Why does shallow surface cultivation prevent evaporation ? 

327 



328 SOILS AND FERTILIZERS 

29. Why is it necessary to cultivate the soil after a rain ? 30. Ex- 
plain the movement of the soil water after a light shower. 31 . What 
influence has rolling the land upon the moisture content of the soil? 
32. What is subsoiling and how does it influence the moisture 
content of soils ? 33. What influence does early spring plowing 
exert upon the soil moisture ? 34. What is the action of a mulch 
upon the soil ? 35. Why should different soils be plowed to differ- 
ent depths ? 36. What is meant by the permeability of a soil? 
37. How may cultivation influence permeability? 38. How may 
commercial fertilizers influence the water content of soils ? 39. 
Explain the physical action of well-prepared farm manures upon the 
soil and their influence upon the soil water. 40. What is the object 
of good drainage ? 41. Why does deforesting a region unfavorably 
influence the agricultural value of a country ? 42. What are the 
sources of heat in soils ? 43. To what extent does the color of 
soils influence the temperature ? 44. What is the specific heat of 
soils? 45- To what extent does drainage influence soil tempera- 
ture and how does cultivation affect soil temperature ? 46. How 
do manured and unmanured lands compare as to temperature ? 47. 
What relation does heat bear to crop growth ? 48. What materials 
impart color to soils ? 49. What is the effect of loss of organic 
matter upon the color of soils ? 50. What materials impart taste to 
soils ? Odor ? 51. What effect does a weak current of electricity 
have upon crop growth ? 52. Do all soils possess the same power 
to absorb gases ? Why ? 

CHAPTER II 

53. What is agricultural geology ? 54. What agencies have 
taken part in soil formation ? 55. How does the action of heat, 
cold, air, and gases aid in soil formation ? 56. Explain the physical 
action of water in soil formation. Explain its chemical action. 57. 
What is glacial action, and how has it been an important factor in 
soil formation ? 58. Explain the action of earthworms and vegeta- 
tion upon soils. 59. How have micro-organisms aided in soil forma- 



REVIEW QUESTIONS 329 

tion ? 60. Explain the terms : sedentary, transported, alluvial, 
colluvial, volcanic, and wind-formed soils. 61. What is feldspar 
and what kind of soil does it produce ? 62. Give the general 
composition of the following rocks and minerals and state the 
kind of soil which each produces : granite, mica, hornblende, 
zeolites, kaolin, apatite, and limestone. 

CHAPTER III 

63. What elements are liable to be the most deficient in soils ? 
64. Name the acid- and base-forming elements present in soils. 65. 
What are the elements most essential for crop growth ? 66. State 
some of the different ways in which the elements present in soils 
combine. 67. Why is it customary to speak of the oxides of the 
elements and to deal with them rather than with the elements ? 68. 
Do the elements exist in the soil in the form of oxides ? 69. What 
are double silicates ? 70. In what forms does carbon occur in soils .'' 
71. Is the soil carbon the source of the plant carbon ? 72. What 
can you say regarding the occurrence and importance of the sulphur 
compounds ? 73. What influence would o.io per cent chlorine have 
upon the soil ? 74. In what forms does phosphorus occur in 
soils? 75. What is the principal form in which nitrogen occurs 
in soils ? 76. What can be said regarding the hydrogen and 
oxygen of the soil ? ']']. State the principal forms and the value as 
plant food of the following elements : aluminum, potassium, calcium, 
sodium, and iron. 78. For plant-food purposes, what three 
divisions are made of the soil compounds ? 79. Why are the 
complex silicates of no value as plant food ? 80. Give the relative 
amounts of plant food in the three classes. 81. How is a soil 
analysis made ? 82. What can be said regarding the economic 
value of a soil analysis ? 83. What are some of the important facts 
to observe in interpreting results of soil analysis ? 84. Under what 
conditions are the results most valuable ? 85. Do the terms ' volatile 
matter' and 'organic matter' mean the same ? 86. How may organic 
acids be employed in soil analysis ? 87. Why are dilute organic 



330 SOILS AND FERTILIZERS 

acids used ? 88. Is the plant food equally distributed in both sur- 
face and subsoil ? 89. Do different grades of soil particles, from 
the same soil, have the same composition? 90. What are 'alkali 
soils'? 91. Why is the alkali sometimes in the form of a crust? 
What is black alkali ? 92. Are all soils with white coating strongly 
alkaline? 93. Give the treatment for improving an alkali soil. 94. 
How may a small 'alkali spot' be treated? 95. What are the 
sources of the organic compounds of soils ? What are acid soils ? 
96. How may the organic compounds of the soil be classified ? 97. 
Explain the term 'humus.' 98. How is the humus of the soil ob- 
tained ? 99. What is humification ? What is a humate ? How 
are humates produced in the soil ? 100. Explain how different 
materials produce humates of different value. loi. Arrange in 
order of agricultural value the humates produced from the following 
materials : oat straw, sawdust, meat scraps, sugar, clover. 102. Of 
what value are the humates as plant food ? 103. How much plant 
food is present in soils in humate forms ? 104. What agencies cause 
a decrease of the humus content of soils ? 105. To what extent 
does humus influence the physical properties of soils ? 106. What 
is humic acid ? 107. What soils are most liable to be in need 
of humus? When are soils not in need of humus ?_ 108. In what 
ways does the humus of long-cultivated soils differ from that of new 
soils ? 109. How may different methods of farming influence the 
humus content of soils ? 

CHAPTER rV 

110. What may be said regarding the importance of nitrogen as 
plant food ? in. What are the functions of nitrogen in plant nu- 
trition ? 112. How may the foliage indicate a lack or an excess of 
this element ? 113. In what three ways did Boussingault conduct 
experiments relating to the assimilation of the free nitrogen of the 
air? 114. What were his results? 115. What conclusions did 
Ville reach ? 116. Give the results of Lawes and Gilbert's experi- 
ments. 117. How did field results compare with laboratory experi- 



REVIEW QUESTIONS 331 

ments ? Ii8. In what ways were the conditions of field experi- 
ments different from those conducted in the laboratory ? 119. Give 
the results of Hellriegel's and Wilfarth's experiments. 120. What 
is noticeable regarding the composition of clover-root nodules ? 121. 
Of what agricultural value are the results of Hellriegel ? 122. What 
is the source of the soil's nitrogen ? 123. How may the organic 
nitrogen compounds of the soil vary as to complexity? 124. To 
what extent may the nitrogen in soils vary ? 125. To what extent 
is nitrogen removed in crops? 126. To what extent are nitrates, 
nitrites, and ammonium compounds found in soils ? 127. To what 
extent is nitrogen returned to the soil in rain water ? 128. How 
may the ratio of nitrogen to carbon vary in soils ? Of what agricul- 
tural value is this ratio ? 129. Under what conditions do soils gain 
in nitrogen content ? 130. What methods of cultivation cause the 
most rapid decline in the nitrogen content of soils, and how can a 
nitrogen equilibrium be maintained in the soil ? 131. What is 
nitrification ? 132. What are the conditions necessary for nitrifica- 
tion, and what are the food requirements of the nitrifying organ- 
ism ? 133. Why is oxygen necessary for nitrification ? 134. How 
do temperature, moisture, and sunlight influence this process ? 
135. What part do calcium carbonate and other basic compounds 
take in nitrification ? 136. How is nitrous acid produced ? 137. 
What is denitrification ? 138. What other organisms are present in 
soils besides those which produce nitrates, nitrites, and ammonia ? 

139. What chemical products do these various organisms produce ? 

140. Why are soils sometimes inoculated , with organisms ? When 
is this necessary and when is it not ? 141. Why does summer 
fallowing of rich land cause a loss of humus and nitrogen ? 142. 
What influence have deep and shallow plowing, and spring and fall 
plowing, upon the available soil nitrogen ? 143. Into what three 
classes are nitrogenous fertiHzers divided ? 144. How is dried blood 
obtained ? What is its composition, and how is it used ? 145. 
What is tankage ? How is it used, and how does it differ in com- 
position from dried blood ? 146. What is flesh meal ? 147. What 



332 SOILS AND FERTILIZERS 

is fish-scrap fertilizer, and what is its comparative value ? 148. 
What seed residues are used as fertilizer ? What is their value ? 
149. What methods are employed to detect the presence of leather, 
hair, and wool waste in fertilizers ? Why are these materials objec- 
tionable ? 150. How may peat and muck be used as fertilizers? 
151. What is sodium nitrate ? How is it used, and what is its value 
as a fertilizer? 152. How does ammonium sulphate compare in 
fertilizer value with nitrate of soda ? What is calcium cyanamid ? 
153. What is the difference between the nitrogen content and the 
ammonia content of fertilizers ? 

CHAPTERS V AND VI 

154. What is fixation ? What is absorption ? Give an illus- 
tration. 155. To what is fixation due ? 156. What part does 
humus take in fixation ? 157. Why do soils differ in fixative 
power ? Why are nitrates not fixed ? Explain the fixation of 
potash, phosphate, and ammonium compounds. 158. Why is fixa- 
tion a desirable property of soils ? 159. Why is it necessary to 
study the subject of fixation in the use of manures ? Why is the 
soil solution dependent upon the fixative power of the soil ? 160. 
Why are farm manures variable in composition? 161. What is 
the distinction between the terms 'stable manure' and 'farmyard 
manure'? 162. About what per cent of nitrogen, phosphoric acid, 
and potash is present in ordinary manure ? 163. Coarse fodders 
cause an increase of what element in the manure ? 164. What 
four factors influence the composition and value of manure ? 165. 
What influence do absorbents have upon the composition of 
manures ? 166. What advantages result from the use of peat and 
muck as absorbents ? 167. Compare the value of manure produced 
from clover with that from timothy hay. 168. How may the value 
of manure be determined from the nature of the food consumed ? 
169. To what extent is the fertility of the food returned in 
the manure ? 170. Is much nitrogen added to the body during the 
process of fattening ? 171. Explain the course of the nitrogen of 



I 



REVIEW QUESTIONS 333 

the food during digestion and the forms in which it is voided in 
the manure. 172. Compare the solid and liquid excrements as to 
constancy of composition and amounts produced. 173. What is 
meant by the manurial value of food ? 174. Name five foods with 
high manurial value ; also five with low manurial value. 175. 
What is the usual commercial value of manures compared with 
commercial fertilizers ? 176. How does the manure from young 
and from old animals compare as to value ? 177. How much 
manure does a well-fed cow produce per day ? 178. What are the 
characteristics of cow manure ? How do horse manure and cow 
manure differ as to composition, character, and fermentability ? 
179. What are the characteristics of sheep manure ? 180. How 
does hen manure differ from any other manure .'' 181. Why should 
the solid and liquid excrements be mixed to produce balanced 
manure? 182. What volatile nitrogen compound may be given off 
from manure ? 183. What may be said regarding the use of human 
excrements as manure ? 184. Is there any danger of immediate 
scarcity of plant food to necessitate the use of human excrements 
as manure ? 185. To what extent may losses occur when manures 
are exposed in loose piles and allowed to leach for six months ? 
186. What two classes of ferments are present in manure ? How 
does an application of farm manure affect the bacterial content of 
soil and what influence does this have upon the plant food of the 
soil ? 187. Explain the workings of the two classes of ferments 
found in manures. 188. How much heat may be produced in 
manure during fermentation ? 189. Is water injurious to manure ? 
190. How should manure be composted ? What is gained ? 191. 
How does properly composted manure compare in composition with 
fresh manure ? 192. Explain the action of calcium sulphate in the 
preservation of manure. 193. How does manure produced in 
barn yards compare in composition and crop-producing value with 
that produced in covered sheds ? 194. When may manure be 
taken directly to the field and spread ? 195. How may coarse 
manures be injurious to crops ? 196. What is gained by manuring 



334 SOILS AND FERTILIZERS 

pasture land ? 197. Is it economical to make a number of small 
manure piles in a field ? Give reason. 198. At what rate per 
acre may manure be used ? 199. To what crops is it not advisable 
to add stable manure ? 200. How do a crop and the manure pro- 
duced from that crop compare in manurial value ? 201. Why do 
manures have such a lasting effect upon soils ? 202. Why does 
manure from different farms vary so much in value and composi- 
tion ? 203. In what ways may stable manures be beneficial ? 

CHAPTER VII 

204. What may be said regarding the importance of phosphorus 
as plant food ? What function does it take in plant economy ? 
205. What is phosphoric acid and how much is removed in ordi- 
nary farm crops ? 206. To what extent is phosphoric acid present 
in soils ? 207. What are the sources of the soil's phosphoric acid ? 

208. What are the commercial sources of phosphate fertilizers ? 

209. Name the four calcium phosphates and give their relative fer- 
tilizer values. 210. Define reverted phosphoric acid. 211. Define 
available phosphoric acid. 212. In what forms do phosphate 
deposits occur ? 213. State the general composition of phosphate 
rock. 214. Explain the process by which acid phosphates are made. 
Give reactions. 215. How is the commercial value of phosphoric 
acid determined ? 216. What is basic phosphate slag and what is 
its value as a fertilizer ? 217. What is guano ? 218. How do raw 
bone and steamed bone compare as to field value ? As to composi- 
tion ? 219. What is dissolved bone ? 220. How is bone black 
obtained, and what is its value as a fertilizer 1 221. How are 
phosphate fertilizers applied to soils ? In what amounts ? 222. 
How may the phosphoric acid of the soil be kept in available 
condition ? 

CHAPTER VIII 

223. What is the function in plant nutrition of potassium ? 224. 
What is potash and to what extent is it removed in farm crops ? 
225. To what extent is potash present in soils .'' 226. What are 



r REVIEW QUESTIONS 335 

the sources of the soil's potash ? 227. What are the various sources 
of the potash used for fertilizers ? 228. What are the Stassfurt salts, 
and how are they supposed to have been formed ? 229. What is 
kainit ? 230. How much potash is there in hard wood ashes ? 231. 
In what ways do ashes act on soils ? 232. How do unleached ashes 
differ from leached ashes ? 233. What is meant by the alkalinity 
of an ash ? 234. Of what value, as fertilizer, are hard- and soft- 
coal ashes ? 235. What is the fertilizer value of the ashes from 
tobacco stems ? 236. Cottonseed hulls ? 237. Peat-bog ashes ? 
238. Sawmill ashes ? 239. Lime-kiln ashes ? 240. How is the 
commercial value of potash determined ? 241 . How are potash 
fertilizers used ? 242. Why is it sometimes necessary to use a lime 
fertilizer in connection with a potash fertilizer ? 

CHAPTER IX 

243. What can be said regarding the importance of calcium as a 
plant food ? 244. What is lime, and to what extent is it removed 
in crops ? 245. To what extent do soils contain lime ? 246. What 
are the lime fertilizers ? 247. Explain the physical action of lime 
fertilizers. 248. Explain the action of lime on heavy clays. 249. 
On sandy soils. 250. In what ways, chemically, do lime fertilizers 
act? 251. How may Ume aid in liberating potash ? 252. What is 
marl ? 253. How are lime fertilizers applied ? 254. What is the 
result when land plaster is used in excess ? 255. Explain the action 
of salt on soils. 256. When would it be desirable to use salt as a 
fertilizer ? 257. Is soot of any value as a fertilizer ? Explain its 
action. 258. Are seaweeds of any value as fertilizer ? What is the 
fertilizer value of street sweepings ? Of garbage ? 

CHAPTER X 

259. What is a commercial fertilizer? An amendment? 260. 
To what does the commercial fertilizer industry owe its origin? 

261. Why are commercial fertilizers so variable in composition? 

262. Explain how a commercial fertilizer is made. 263. Why are 



336 SOILS AND FERTILIZERS 

analysis and inspection of fertilizers necessary? 264. What are 
the usual forms of nitrogen in commercial fertilizers? 265. Of 
phosphoric acid and potash? 266. How is the value of a commer- 
cial fertilizer determined? 267. What is gained by home mixing 
of fertilizers? 268. What can be said about the importance of 
tillage when fertilizers are used? 269. How are commercial fer- 
tilizers sometimes injudiciously used? 270. How may field tests 
be conducted to determine a deficiency in available nitrogen, phos- 
phoric acid, or potash? 271. To determine a deficiency of two 
elements? 272. How are the preliminary results verified? 273. 
Why is it essential that field tests with fertilizers be made? 274. 
Under what conditions does it pay to use commercial fertilizers? 
275. What is the result when commercial fertilizers are used in 
excessive amounts? 276. Under ordinary conditions, what special 
help do the following crops require : wheat, barley, corn, potatoes, 
mangels, turnips, clover, and timothy? 277. In what ways do 
commercial fertilizers and farm manures differ? How do they com- 
pare in crop-producing value ? 

CHAPTER XI 

278. Does the amount of fertility removed by crops indicate the 
nature of the fertilizer required? In what ways are plant-ash 
analyses valuable? 279. Explain the action of plants in rendering 
their own food soluble. To what extent does the soil solution sup- 
ply plant food ? 280. Why do crops differ as to their power of pro- 
curing food? 281. Why is vi^heat grown on a clay soil less liable 
to need potash than nitrogen? 282. What position should wheat 
occupy in a rotation? 283. In what ways do wheat and barley 
differ in feeding habits ? 284. What can be said regarding the food 
requirements of oats? 285. Corn removes from the soil twice as 
much nitrogen as a wheat crop, yet wheat usually thrives after 
corn. Why? What help is corn most liable to need in the way 
of food? 286. What is flax wilt? 287. What position should flax 
occupy in a rotation? 288. On what soils does flax thrive best? 



REVIEW QUESTIONS 337 

289. What is the essential point to observe in the manuring of 
potatoes? 290. What kind of manuring is required by sugar beets ? 
291. Why should the manuring of mangels be different from that of 
turnips? 292. What may be said regarding the food requirements 
of buckwheat and rape? 293. What kind of manuring do hops and 
cotton require? 294. What kind of manuring is most suitable for 
leguminous crops ? For garden crops, for orchards, and lawns ? 

CHAPTER XII 

295. What is the object of rotating crops? 296. Should the 
whole farm undergo the same rotation system? 297. What is 
meant by soil exhaustion? 298. What are the important princi- 
ples to be observed in a rotation? 299. Explain why it is 
essential that deep- and shallow-rooted crops should alternate? 
300. Why is it necessary that humus be considered in a rota- 
tion? 301. What is the object of growing crops of dissimilar feed- 
ing habits? 302. How may crop residues be used to the best 
advantage? 303. How is decline of soil nitrogen prevented by 
a good rotation of crops? 304. In what ways do different 
crops and their cultivation influence the mechanical condition 
of the soil? 305. How may the best use be made of the soil 
water? 306. How may a rotation make an even distribution of 
farm labor ? 307. How are manures used to the best advantage in 
a rotation? 308. In what other ways are rotations advantageous? 

309. What may be said regarding long- and short-course rotations? 

310. How is the conservation of fertility best secured ? 311. Why 
does the use made of crops influence fertility? 312. What are the 
essential points to be observed in the two systems of farming com- 
pared in Section 344? 313. Is it essential that all elements re- 
moved in crops be returned to the soil in exactly the amounts 
contained in the crops? Why? 314. How does manure influence 
the inert matter of the soil? 315. What general systems of 
farming best conserve fertility? 316. Under what conditions 
may farms be gaining in reserve fertihty? 317. Why in continued 

z 



338 SOILS AND FERTILIZERS 

grain culture does the loss of nitrogen from a soil exceed the 
amount removed in the crop? Will a crop rotation alone maintain 
the fertility of the soil ? 

CHAPTER XIII 

318. Why do soils need further treatment than plowing for the 
preparation of the seed bed? 319. Why should different soils receive 
different methods of treatment in the preparation of the seed bed? 
320. How would you determine the best treatment to give a soil for 
the preparation of the seed bed? 321. How do different methods of 
plowing influence the condition of the seed bed? 322. Why does 
complete inversion of sod frequently form a poor seed bed? 323. 
How should the plowing be done to form a good seed bed? 324. 
Why is it economy to pulverize the soil as much as possible when 
it is plowed? 325. What effect does the moisture content of the 
soil at the time of plowing have upon the condition of the seed 
bed? 326. What effect does an excess of moisture have upon the 
plowing and working of clay soils? 327. In what condition should 
the seed bed be left as to fineness? 328. What is gained by fining 
and moderately firming the seed bed? 329. Why is aeration of 
the soil necessary? 330. Why do different soils require different 
degrees of aeration? 331. Under what conditions can the seed 
bed be prepared without plowing? 332. On what kinds of soil is 
such a practice not advisable? 333. When is it advisable to mix 
the subsoil with the surface soil? 334. When is it not desirable 
to mix the surface soil and subsoil? 335. How can the plowing 
and cultivation of the soil best be carried on to destroy weeds? 
336. In what way does cultivation influence bacterial action in the 
soil? 337. What classes of compounds in the soil are subject to 
bacterial action? 338. How does the action of bacteria affect the 
supply of available plant food? 339. What is meant by inocu- 
lation of soils? 340. In what two ways can this be accomplished? 
341. What soils are most improved by inoculation? 342. What 
soils are least in need of inoculation ? 347. What other treatment 
must often be combined with inoculation? 344. Why do different 



1 REVIEW QUESTIONS 339 

crops require different cultivation? 345. How can the best kind of 
cultivation for a crop be determined? 346. How can soils best be 
cultivated to prevent washing and gullying? 347, What treatment 
should such soils receive to be permanently improved? 348. What 
relationship exists between bacterial diseases of soils and of crops ? 
349. What treatment should soils receive to prevent bacterial 
diseases? 350. How can the spreading of bacterial diseases 
through infected seed be prevented? 351. Why must the sanitary 
condition of a soil be considered? 352. What are the effects of some 
forms of fungi upon soils? 353. In what way does thick or thin 
seeding affect plant growth? 354. What effect does abnormal 
crowding of plants have upon growth? 355. How would you deter- 
mine the amount of seed for crop production? 356. How would 
you determine the most suitable crop for any soil ? 357. What should 
be the aim in selecting crops for soils? 358. Why should the crop 
selected vary with diiferent types of soil? 359. What is the in- 
herent fertility of soils? 360. What is the cumulative fertility of 
soils? 361. How can the total fertility of soils be best increased? 
362. Describe soils of the highest fertility. 363. Why must the 
amount of plant food as well as the physical condition of the soil be 
considered in the improvement of soils? 364. What relation does 
the fertility of the soil bear to any agricultural system ? 



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6. Wiley : Agricultural Analysis, Vol. I. 

7. Hilgard : Soils. 

8. Maryland Agricultural Experiment Station Bulletin No. 21. 

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10. Osborne : Journal of Analytical Chemistry, Vol. II, Part 3. 

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20. Merrill : Rocks, Rock-weathering, and Soils. 

340 



REFERENCES 34 I 

21. MuNTZ : Comptes Rendus de rAcademie des Sciences, CX 

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25. Peter : Association of Official Agricultural Chemists Report, 

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26. Loughridge : American Journal of Science, Vol. VII (1874). 

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29. Mulder : From Mayer ; Lehrbuch der Agrikulturchemie, 2. 

30. Wheeler : Rhode Island Agricultural Experiment Station 

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31. Year-book U. S. Department Agriculture, 1895. 

32. Loughridge : South Carolina Agricultural Experiment Station 

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33. Association of Official Agricultural Chemists Report, 1893. 

34 Washington Agricultural Experiment Station Bulletin No. 13. 

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37. Snyder : Minnesota Agricultural Experiment Station Bulletin 

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38. Snyder : Minnesota Agricultural Experiment Station Bulletin 

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39. Lawes and Gilbert : Experiments on Vegetation, Vol. I. 

40. BoussiNGAULT : Agronomic, Tome I. 

41. Atwater : American Chemical Journal, Vol. VI, No. 8, and 

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42. Hellriegel : Welche StickstofFe Quellen stehen der Pflanze 

zu Gebote ? 



342 SOILS AND FERTILIZERS 

43. Snyder : Minnesota Agricultural Experiment Station Bulletin 

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44. Warington : U. S. Department of Agriculture, Office of Ex- 

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45. HiLGARD : Association of Official Agricultural Chemists Re- 

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46. Marchal : Journal of the Chemical Society (abstract), June, 

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47. KiJNNEMANN : Die Landwirthschaftlichen Versuchs-Stationen, 

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48. Adametz : Abstract, Biedermann's Centralblatt fiir Agrikultur- 

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49. Atwater : American Chemical Journal, Vol. IX (1887). 

50. Stutzer : Biedermann's Centralblatt fiir Agrikulturchemie,i883. 

51. Jenkins : Connecticut State Agricultural Experiment Station 

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52. Bulletin 107, U. S. Department of Agriculture, Bureau of Chem- 

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53. Journal of the Royal Agricultural Society, 1850. 

54. From Sachsse : Lehrbuch der Agrikulturchemie. 

55. Lawes and Gilbert : Experiments with Animals. 

56. Beal : U. S. Department of Agriculture, Farmers' Bulletin 

No. 21. 

57. Snyder : Minnesota Agricultural Experiment Station Bulletin 

No. 26. 

58. Mainly from Armsby : Pennsylvania Agricultural Experiment 

Station Report, 1890. Figures for grains calculated from 
original data. 

59. Heiden : Dungelehre.i 

60. LiEBiG : Natural Laws of Husbandry. 

61. Cornell University Agricultural Experiment Station Bulletins 

Nos. 13, 27, and 56. 

62. KiNNARD : From Manures and Manuring by Aikman. 

63. Wyatt : Phosphates of America. 



t 



REFERENCES 343 

64. Wiley : Agricultural Analysis, Vol. III. 

65. GoESSMANN : Massachusetts Agricultural Experiment Station 

Report, 1894. 

66. Connecticut (State) Agricultural Experiment Station Bulletin 

No. 103. 

67. GoESSMANN : Massachusetts Agricultural Experiment Station 

Report, i8g6. 

68. LiPMAN AND VooRHEES : U. S. Department of Agriculture, 

Office of Experiment Stations Bulletin 194. 

69. BoussiNGAULT : From Stoker : Agriculture. 

70. Handbook of Experiment Station Work. 

71. New York (State) Agricultural Experiment Station Bulletin 

No. 108. 

72. Voorhees : U. S. Department of Agriculture, Farmers' Bulle- 

tin No. 44. 

73. LiEBiG : Die Chemie in ihrer Anwendung auf Agrikultur und 

Physiologic. 

74. Warington : Chemistry of the Farm. 

75. Lawes and Gilbert : Growth of Wheat. 

76. Lawes and Gilbert : Growth of Barley. 

']']. Lugger : Minnesota Agricultural Experiment Station Bulle- 
tin No. 13. 

78. Lawes and Gilbert : Growth of Potatoes. 

79. Snyder : Minnesota Agricultural Experiment Station Bulletin 

No. 56. 

80. Shaw : U. S. Department of Agriculture, Farmers' Bulletin 

No. II. 

81. White : U. S. Department of Agriculture, Farmers' Bulletin 

No. 48. 

82. Lawes and Gilbert : Permanent Meadows. 

83. Thompson, Porteus : Graduating Essay, Minnesota School of 

Agriculture. 

84. Nefedor : Abstract, Experiment Station Record, Vol. X, 

No. 4. 



344 SOILS AND FERTILIZERS 

85. Snyder : Minnesota Agricultural Experiment Station Bulletin 

No. 89. 

86. Conn : Agricultural Bacteriology. 

87. New York Agricultural Experiment Station Bulletins Nos. 

270, 282. 

88. Meyer : Outlines of Theoretical Chemistry. 

89. VoORHEES : Fertilizers. 

90. Cornell University Experiment Station Bulletin No. 103. 

91. FRAPS : Annual Report 1904, Association Official Agricultural 

Chemists. 

92. Illinois Experiment Station Bulletin No. 93. 

93. Canadian Experiment Farms Report, 1903, etc. 

94. D. Land. Vers. Stat., 1899, 52. 

95. A. D. Hall : The Soil. 

96. Snyder: Minnesota Experiment Station Bulletin No. 109. 

97. King : Investigations in Soil Management. 

98. Ohio Agricultural Experiment Station Bulletin No. no. 



INDEX 



Absorbents, i6o. 

Absorption, of heat by soils, 47; of 

gases by soils, 320. 
Absorptive power of soils, 47, 51. 
Acid phosphate, preparation of, 323. 
Acids in plant roots, 258. 
Acid soils, 1 01. 

Acid soluble matter of soils, 81, 320. 
Aeration of soils, 275. 
Aerobic ferments, 177. 
Agricultural geology, 54. 
Agronomy, 9. 
Air and soil formation, 60. 
Air movement through soils, 314. 
Albite, 65. 
Alchemy, i. 
Alkaline soils, 96. 
Alkali soils, improving, 99. 
Aluminum of soils, 78. 
Amendments, soils, 233. 
Ammonium compounds, 130. 
Ammonium sulphate, 155. 
Anaerobic ferments, 177. 
Analysis of soils, how made, 87; 

value of, 88, 90; interpretation of, 

91-92. 
Apatite rock, 67. 
Apparatus, list of, 308. 
Application, of fertilizer, 252; of 

manures, 181, 184. 
Arrangement of soil particles, 18. 
Ashes, 218; action of, on soils, 219; 

testing of, 324. 
Assimilation, of nitrogen, 116; of 

phosphates, 199. 
Atmospheric nitrogen, n8. 
Atwater, 122, 151. 



Availability of plant food, 92. 
Available nitrogen, 128, 152. 
Available phosphate, 203, 210. 

Bacterial action and cultivation, 138, 

298. 
Barley, fertilizers for, 253; food 

requirements of, 261. 
Blood, dried, 147. 
Bone, dissolved, 208; steamed, 208; 

fertilizers, 207. 
Bone ash, 208. 
Bone black, 209. 
Boussingault, 11, 119, 120. 
Buckwheat, food requirements of, 266. 



Calcium as essential element, 223. 

Calcium carbonate, and nitrification, 
140; compounds of soils, 79; ni- 
trate and cyanamid, 156; phos- 
phate, 68. 

Capillarity, 30; and cultivation, 36. 

Capillary water, determination of, 
312. 

Carbon, of soil, 74; sources for plant 
growth, 74. 

Cavendish, 2. 

Cereal crops, 259. 

Chemical composition of soils, 71. 

Chlorine of soil, 75. 

Citric acid, use of, in soil analysis, 84. 

Classification, of soils, scheme for, 
326; of elements, 71. 

Clay, formation of, 67; particles, 16; 
sedimentation of, 317. 

Clover, as manure, 154; nitrogen 

345 



346 



INDEX 



returned by, 122, 134, 289; root 
nodules, 125; manuring of, 269. 

Coal ashes, 220. 

Color, of plants, influenced by nitro- 
gen, 118; of soils, 47, 50; and soil 
temperature, 314. 

Combination of elements in soils, 72. 

Commercial fertilizers, 233, 254; 
abuse of, 245; and tillage, 244; 
and farm manures, 254; compo- 
sition of, 234; extent of use, 233; 
field tests with, 248; for special 
crops, 253; home mixing of, 243; 
inspection of, 237; judicious use 
of, 246; mechanical condition of, 
238; misleading statements, 241; 
nitrogen of, 238; phosphoric acid 
of, 239; plant food in, 237; potash 
of, 240; preparation of, 234; 
valuation of, 241 ; variable com- 
position, 234. 

Composition, of soils, 95, 97, 98; of 
manures, 1 59. 

Composting manures, 178. 

Corn, fertilizers for, 254; food re- 
quirements of, 263; and manure, 
185; soils, 23. 

Cotton, fertilizers for, 267. 

Cottonseed meal, 151. 

Cow manure, 170. 

Crop residue, 275. 

Cultivation, after rains, 38; and bac- 
terial action, 298; shallow surface, 
37; and soil moisture, 313; and 
soil temperature, 49. 

Cumulative fertility, 304. 

Cyanamid, 156. 

Davy, work of, 3. 

Deficiency, of nitrogen, 249; of 
phosphoric acid, 250; of potash, 
250; of two elements, 250. 

Denitrification, 141. 

De Saussure, work of, 3, 118. 

Dilute mineral acids, action of, 84. 



Diseases of soils, 301. 
Dissolved bone, 208. 
Distribution of soils, 62. 
Drainage, 34, 47, 300. 
Dried blood, 147. 

Early truck soUs, 22. 
Earthworms, 61. 
Electricity of soU, 52. 
Evaporation, 53; heat required for, 

46. 
Excessive use of fertilizers, 252. 
Experimental plots, 248. 
Experiments, 310, 325. 
Exposure and soil temperature, 49. 

Fallow fields, 145. 

Fall plowing, 41. 

Farm manures, 158, 189; and com- 
mercial fertilizers, 254. 

Feldspar, 64, 237. 

Fermentation of manures, 177. 

Fertility, conservation of, 285; im- 
portance of, 305 ; removed in 
crops, 254. 

Fertilizers, amount to use, 252; in- 
fluence upon soil water, 44; on 
barley, 253; on wheat, 253. 

Field tests with fertilizers, 248. 

Fine earth, 14. 

Fish fertilizer, 151. 

Fixation, 191; of ammonia, 194; of 
phosphates, 192; of potash, 192; 
due to zeolites, 191; nitrates not 
fixed, 193; and available plant 
food, 194. 

Flax, food requirements of, 264; soils, 

24- 

Flesh meal, 1 50. 

Forest fires, in. 

Formation of soils, 54, 62. 

Form of soil particles, 17. 

Fruit soils, 23. 

Fruit trees, fertilizers for, 270. 



INDEX 



347 



Gains, of humxis, 114; of nitrogen, 

133- 
Garden crops, fertilizers for, 269. 
Geological study of soil, value of, 69. 
Gilbert, 7. 

Glaciers, action of, 57. 
Grain soils, 24. 
Granite, 66. 

Grass lands, fertilizers for, 268. 
Grass soils, 24. 
Guano, 207. 
Gullying of soils, 300. 
Gypsum and manure, 179. 

Hair, 152. 

Hay land, fertilizing, 268. 

Heat, and crop growth, 50; pro- 
duced by manures, 178; of soil, 46, 
50; required for evaporation, 46. 

Heiden, 174, 180. 

Hellriegel, 22, 28, 123. 

Hen manure, 172. 

Hog manure, 172. 

Hops, fertilizers for, 267. 

Hornblende, 65. 

Horse manure, 1 70. 

Human excrements, 174. 

Humates, 103; as plant food, 107. 

Humic acid, 112. 

Humic phosphates, 105, 210. 

Humification, 104. 

Humus, 103; active and inactive, 114; 
causes fixation, 192; composition 
of, 106; extraction of, trom soils, 
321; loss of, from soils, 11 1; soils 
in need of, 113. 

Hydrogen, compounds of soil, 77. 

Hydroscopic moisture, 32; deter- 
mination of, 310. 

Importance of field trials, 251. 
Income and outgo of fertility, 286, 290. 
Infected seed and soU diseases, 301. 
Inherent fertility, 304. 
Injury of coarse manures, 46, 182. 



Inoculation of soUs, 143. 
Insoluble matters of soils, 82. 
Iron compounds of soil, 80. 

Jenkins, 152. 

Kainit, 179, 216, 243. 
Kaolin, 67. 
King, 37, 40, 41. 

Laboratory note- book, 307; practice, 

308, 326. 
Lawes and Gilbert, 6, 121, 122, 260. 
Lawn fertilizers, 272. 
Leached ashes, 219. 
Leaching of manure, 175. 
Leather, 152. 
Leguminous crops, fertilizers for, 

269; as manure, 154; nitrogen 

assimilations of, 122, 125. 
Liebig, 5, 6, 174, 257. 
Lime, action on soils, 225; amount 

of, in soils, 224; amount removed 

in crops, 224; excessive use of, 229; 

fertilizers, 225; indirect action of, 

227; physical action of, 228; 

stone, 68; use of, 229; lime and 

acid soil, 226; and clover, 226. 
Liquid manure, 164. 
Loam soils, 27. 
Loss, of fertility in grain farming, 287; 

of humus, hi; of nitrogen, 132, 

145- 
Losses from manures, 176-177. 

Magnesium compounds of soils, 79. 

Magnesium salts as fertilizers, 230. 

Mangels, fertilizers for, 254. 

Manure, from cow, 170; hen, 172; 
hog, 172; horse, 170; sheep, 171. 

Manures, farm, 158; composition of, 
159; composting of, 178; crop 
producing value, 168; direct ap- 
plication of, 181; fermentation of, 
177; influence of, on soil tempera- 



348 



INDEX 



ture, 313; on moisture, 313; in- 
fluenced by foods, 162; influenced 
by age and kind of animal, 1 6g ; 
leaching of, 175; liquid, 164; 
mixing of, 173; solid, 164; and 
soil water, 45, 112; and tempera- 
ture, 48; preservation of, 175; 
use of, 181, 184; use of, in rotation, 
278; value of, 189; volatile prod- 
ucts from, 173. 

Manurial value of foods, 167. 

Manuring, of crops, 185; pasture 
land, 183. 

Marl, 228. 

Mechanical, analysis of soils, 19; 
condition of fertilizers, 238; compo- 
sition of soil types, 27. 

Methods of farming, influence of, 
upon fertility, 114. 

Mica, 66. 

Micro-organisms and soil formation, 
54, 60. 

Mineral matter and humus, 109. 

Mixing manures, 173. 

Moisture for nitrification, 139. 

Movement of water after rains, 39. 

Muck, 153, 161. 

Mulching, 42. 

Nitrate of soda, 154. 

Nitric nitrogen, 154.' 

Nitrification, 135; conditions neces- 
sary for, 136; elements essential 
for, 140; and plowing, 145; and 
sunlight, 139. 

Nitrogen, assimilation, 118, 121; of 
clover plant, 122, 125; as plant 
food, 116; compounds of soil, 76; 
compounds, solubility of, 323; 
deficiency of, in soil, 249; gain of, 
in soils, 133-134; loss of, by 
fallowing, 144; losses of, from soil, 
132; ratio of, to carbon, 131; re- 
moved in crops, 128; in com- 
mercial fertilizers, 238; in rain 



water and snow, 131; amount of, 

in soUs, 128; in organic forms, 127; 

as nitrates, 129; as nitrites, 129; 

availability of, 127; forms of, 126; 

origin of, 126. 
Nitrogenous manures, 146, 157. 
Number of soil particles, 19. 

Oats, food requirements of, 262. 

Odor of soils, 51. 

Organic acids, action of, upon soils, 
84, 85. 

Organic compounds of soil, classifi- 
cation of, 103; source of, 102. 

Organic nitrogen, 147, 152. 

Organisms, ammonia- producing, 141; 
of soil, 141; nitrous acid, 140; 
nitrifying, 137; products of, 142. 

Orthoclase, 65. 

Osborne, 20. 

Oxidation of soil, 48. 

Oxygen compounds of soil, 77. 

Oxygen, necessary for nitrification, 138. 

Pasteur, 8. 

Peat, 153, 161. 

Percolation, 32. 

Permanent meadows, manuring of, 
268. 

Permeability of soils, 44. 

Phosphate fertilizers, 198; commer- 
cial forms, 201 ; manufacture of, 
204; as plant food, 198; removed 
by crops, 199; reverted, 202; 
rock, 203; slag, 206; use of, 205. 

Phosphoric acid, of commercial fer- 
tilizers, 201, 239; available, 198, 
203, 210; acid in soils, 200; defi- 
ciency of, 250; removal in crops, 
199; soluble and insoluble in soils, 
84; testing for, 323; value of, 205. 

Phosphorus compounds of soils, 75. 

Physical, analysis of soils, 316. 

Plant food, classes of, 80; ash and 
fertilizers, 256; distribution of, 93, 



INDEX 



349 



94; in soil solution, 8r, 196; total 
and available, 92, 93. 

Plants, crowding of, in seed bed, 302. 

Plowing, depth of, 43; energy re- 
quired for, 293; fall, 41; spring 
41; influence of, on soU, 291; in- 
fluence of, on moisture, 294; influ- 
ences nitrification, 291. 

Pore space, 13. 

Potash fertilizers, 212; use of, 222; 
of commercial fertilizers, 240; salts, 
218. 

Potash, in soils, amount of, 214; 
sources of, 215; soluble and in- 
soluble, 84; and lime, joint use of, 
222; muriate of, 217; sulphate, 
217; removed in crops, 213. 

Potassium compounds of soil, 78. 

Potato, fertilizers for, 264; food 
requirements of, 264; soils, 22. 

Preliminary trials with fertilizers, 248. 

Priestley, 2. 

Property of soils, 1 2 ; modified by 
farming, 115. 

Pulverized lime rock, 227. 

Pulverizing soils, 295. 

Quartz, 64. 
Questions, 327. 

Rainfall and crop production, 29. 
Rape, food requirements of, 266. 
Reaction of soils, determination of, 

319- 

References, 340, 344. 

Relation of crop and soil type, 303. 

Reverted phosphoric acid, 202. 

Review questions, 327. 

Roberts, 43, 175, 293. 

Rock disintegration, 55, 68. 

Rocks, composition of, 64, 69; prop- 
erties of, 318. 

Rolling of soils, 40, 294. 

Root crops, fertilizers for, 266. 

Roots, action on soil, 255, 276. 



Rotation, and soil water, 277; and 
weeds, 280. 

Rotation of crops, 273, 284; prin- 
ciples involved, 274; length of, 281 ; 
problems, 284; and farm labor, 
278; and humus, 275; and insects, 
280; and soil nitrogen, 276. 

Salt as a fertilizer, 229. 

Sand, grades of, 14, 15. 

Schlosing, 8. 

Schubler, 5. 

Seaweeds as fertilizers, 231. 

Sedentary soils, 62. 

Seed, amount of, per acre, 303. 

Seed bed, preparation of, 291. 

Seed residues, 151. 

Sheep manure, 171. 

Silicon and silicates, 74. 

Silt particles, 17. 

Size of soil particles, 14. 

Skeleton of soils, 14. 

Small fruits, fertilizers for, 271. 

Small manure piles, 183. 

Sodium compounds of soils, 80. 

Sodium nitrate, 154. 

Soil, composition of, 97, 98; con- 
servation of fertility, 285; ex- 
haustion, 274, 304; management, 
303; particles, study of, 319; sam- 
pling of, 86, 87; solution of, 80, 196; 
types, 21. 

Soils and agriculture, relation of, 305 ; 
crops suitable for, 303. 

Soot, 230. 

Specific gravity of soil, 13. 

Specific heat of soil, 48. 

Sprengel, s._ 

Spring plowing, 41. 

Stassfurt salts, 216. 

Stock farming and fertility, 288, 

Storer, 75, 148. 

Strand's plant ash, 231. 

Street sweepings, 232. 

Stutzer, 152. 



350 



INDEX 



Subsoiling, 40. 

Sugar beets, and farm manures, 185; 

fertilizers for, 265. 
Sugar beet soils, 24. 
Sulphate of potash, 217. 
Sulphur compounds of soil, 75. 
Superphosphates, 204. 
Surface subsoil, mixing of, 297. 

Tankage, 149. 

Taste of soils, 51. 

Temperature of soils, 46. 

Testing for nitrates, 322. 

Tests with fertilizers, 248. 

Thaer, work of, 3. 

Tobacco, manuring of, 186. 

Tobacco stems, 221. 

Transported soils, 62. 

Truck farming and fertilizers, 269. 

Tull, 8. 

Turnips, fertilizers for, 254, 266. 

Van Helmont, i. 

Vegetation and soil formation, 61. 

Ville, 121. 

Volatilization of ammonium salts, 322. 

Volcanic soils, 64. 

Volume of soils, 13. 

Voorhees, 243, 269. 

Warington, 8, 139. 



Washing of land, 300. 

Water, action of, upon rocks and 
soils, 56; in rock decay, 59; bot- 
tom, 29; capillary, 30; capillary 
conservation of, 36-38. 

Water holding, capacity of soils, 311; 
hydroscopic, 32; losses by evapo- 
ration, 23'> losses by percolation, 
32; losses by transpiration, 34; of 
soil, 29, 34; of soil influenced by 
drainage, 34; by forest regions, 35; 
by manures, 45; by mulching, 42; 
by plowing, 41; by rolling, 40; 
by subsoiling, 40; required by 
crops, 28; soluble matter of soils, 
196. 

Weeds, cultivation to destroy, 297; 
fertility in, 231. 

Weight of soils, 12; how determined, 

313- 
Wheat, fertilizers for, 253; food 

requirements of, 260; soils, 25-26. 
Whitney, 19, 52. 
Wilfarth, 124. 

Wind as agent in soil formation, 62. 
Winogradsky, 8. 
Wood ashes, 218. 
Wool waste, 152, 231. 

Zeolites, 67, 191. 



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